Universities have long turned to wealthy alumni to help finance their athletic departments. Nike founder Phil Knight fueled Oregon’s rise to prominence, for example, and oil tycoon T. Boone Pickens subsidized a building boom at Oklahoma State.

Now universities are increasingly soliciting financial support from a previously untapped cohort of former students: athletes who have gone on to make fortunes in professional sports. And the gifts are getting bigger.

This month, Golden State Warriors star Draymond Green announced a $3.1 million donation to Michigan State’s athletic department — one of the largest sums ever given by an active athlete. But seven-figure philanthropy from pro athletes is becoming more common.

Miami Dolphins defensive tackle Ndamukong Suh pledged $2.6 million from his first NFL contract to the University of Nebraska, and New York Mets outfielder Curtis Granderson gave $5 million to the University of Illinois at Chicago — about half the budget for the Flames’ new baseball stadium. A Georgetown capital campaign attracted million-dollar gifts from NBA players Roy Hibbert and Jeff Green. In June, New Orleans Saints quarterback Drew Brees made his second seven-figure donation to his alma mater, Purdue.

Michigan State’s athletic director, Mark Hollis, said he courted potential donors like Draymond Green while they were still on campus.

“If students don’t understand that there’s others giving them this opportunity, I think that’s a mistake,” Hollis said, adding, “We make sure everyone understands our needs.”

In an interview, Green referred to his recent donation as “kind of a thank you.”

“I went to Michigan State as a boy, a boy who really didn’t know where life was going to take me, really my own identity,” he said. “I left Michigan State a man.”

Pro athletes have long been recognized as valuable assets and recruiting boons to their former college teams. A generation of North Carolina Tar Heels was raised on stories of Michael Jordan’s wearing UNC shorts under his Chicago Bulls uniform, and television cameras are quick to pick out NFL players on the sidelines as they watch their former colleges play. In January, former Texas A&M quarterback Johnny Manziel tweeted at a top high school prospect a week before national signing day, helping secure the prospect’s commitment to the Aggies.

But these days, multimillionaire athletes are supplementing the soft currency they have long given their universities with the hardest currency there is. And university athletic departments, which typically rely on donations for about a quarter of their budgets, are actively soliciting this new class of wealthy alumni.

Rising league revenues have led to higher salaries for many professional players; Green, for example, decided to make his gift shortly after signing a five-year, $82 million contract with the Warriors in July. Endorsement deals have led not only to more income but also to more diversified sources of it, and athletes are increasingly aware of the power and opportunity that money brings.

“If you look around,” Green said, “you see a guy like Ndamukong Suh meeting with Warren Buffett, you see LeBron James and all his different businesses, a Caron Butler. Athletes are really getting more involved in understanding the business side of things.”

This month, Green bumped into Knight when both were in East Lansing, Mich., to watch Oregon’s football team play Michigan State. Knight, who has contributed hundreds of millions of dollars to Oregon, commended Green, who played at Michigan State from 2008 to 2012, for his recent gift.

“It’s nothing like what you’ve done,” Green told Knight, according to Daniel Sillman, one of Green’s advisers, who was present when the men met. “But I’m on my way.”

Knight replied, “It’s a lot more than I did when I was 25 years old.”

As the newly wealthy have done for centuries, athletes see philanthropy as a pathway to respect, new networks and power. Some have been philanthropic in more traditional venues. Hockey star P.K. Subban pledged $10 million to Montreal Children’s Hospital last week. James, a native of Akron, Ohio, did not attend college, but he has promised to pay the tuition of as many as 2,300 children from his hometown if they attend the University of Akron.

“The whole phenomenon of athlete philanthropy is becoming much more formalized and institutionalized,” said Katherine Babiak, a sports management professor at the University of Michigan. “It really is part of the athlete’s brand, their identity, their persona."

Since announcing his gift, Green has been contacted by other top players about how he went about making it, said Sillman, who is the director of business development at RSE Ventures, a sports and entertainment venture firm. Sillman also said he had received calls on behalf of players who were thinking about making similar donations as well as from nonplayers who, like Knight, saw in Green someone they might be doing business with for a long time to come.

“I can’t tell you how many people have reached out from outside of sports asking to spend time with him,” Sillman said.

Increasingly, athletic directors at major universities have wised up to this class of affluent and grateful alumni and former lettermen. Brees’ latest donation to Purdue — he and his wife previously gave $2 million in 2007 — came days after top university and athletic officials held a three-day meeting with former players and alumni to discuss a master plan for investments in the Boilermakers’ football program.

Morgan Burke, Purdue’s athletic director, said he tried to help athletes “understand there’s someone out there paying your scholarships who doesn’t even know you, and if you have the opportunity to join that group, at whatever level your financial capacity allows, you do that.”

A department’s best ambassador is its coach, said Lee Reed, Georgetown’s athletic director.

“John Thompson III has instilled that in them or made that part of their experience,” Reed said, referring to Georgetown’s basketball coach for nine seasons. “It was easier for them to connect the dots, to say, ‘That makes sense for me to give back to the place where I had a good experience.’”

Michigan State has been particularly successful in cultivating former lettermen.

Donors to the Spartans’ athletic programs include basketball player Steve Smith, who gave $2.5 million toward an academic support center that is named for his mother; offensive lineman Flozell Adams; and Magic Johnson, the biggest star the university has produced. Johnson made millions in basketball but multiples more in his subsequent business ventures; he has given at least $4 million to Michigan State.

To some extent, Green is a special case. A native of Saginaw, Michigan, he was a four-year letterman in an era when most basketball stars leave college early. While a student, Green frequently visited Hollis to make suggestions about athlete welfare and campus life.

At the news conference announcing the gift, Spartans coach Tom Izzo said he remembered that Green had tried to see every one of Michigan State’s teams play while he was a student.

Of the $3.1 million in Green’s pledge, only $1 million is dedicated to a specific project. It will endow a strength and conditioning complex in the Breslin Center, the basketball program’s campus home. Green seemed more excited for other things his gift would do.

“My plan is to be the first athlete ever to endow a scholarship,” he said.

Green said he had consulted with Izzo, who is entering his 21st season as coach and who in 2011 — at the outset of Green’s senior season — donated $1 million to the athletic department.

“He said it was one of the happiest moments of his life,” Green said. “I wanted that feeling.”

In addition to eliciting that altruistic sentiment — and more favorable tax treatment — these donations can add to the perception that athletes compete for the love of the game, which is a positive for their brands.

“There’s a huge market of fans who identify with athletes,” said Babiak. “There’s a two-way street: The athlete wants to reinforce that, and the fans want to eat it up.”