Dolphins left guard Richie Incognito is being investigated by the NFL Players Association for harassing teammate Jonathan Martin, according to a report by ESPN.

Martin, a tackle who has lined up next to Incognito for much of the last 1 1/2 seasons, left the club this week after being frustrated by what teammates said were routine locker-room pranks but that others have described as bullying and harassment.

After Thursday night’s 22-20 overtime victory against Cincinnati, players denied that they had harassed Martin to the point that he felt compelled to leave.

But ESPN reported Friday night that, according to sources, “any emotional issues that Martin is experiencing are directly related to his harassment.”

ESPN also said that the NFLPA is conducting a “thorough and detailed review that would extend to the team’s workplace environment.”

Coach Joe Philbin, meeting with reporters Friday, wouldn’t say whether he had witnessed bullying of Martin.

“We emphasize a culture of team first, accountability and respect for each other,” Philbin said in reading from a prepared statement. “Any behavior that deviates from that is inconsistent with the values of our organization.”

During Martin’s first training camp, in August 2012, he was teased by teammates and called “a big weirdo.” Some of those moments were captured on the HBO training-camp documentary “Hard Knocks.” Incognito was a ringleader for the teasing.

This week’s trouble began Monday when teammates pulled a prank on Martin in the cafeteria — getting up from the lunch table when he was the last to sit down. Martin then left the team and has not returned.

He reportedly has sought counseling. He is being excused from the team with a “non-football injury,” according to Philbin.

FoxSports.com reported Thursday night that Martin had been subjected to “excessive, over-the-top-bullying.”

Incognito suffered a neck injury in Thursday’s game and was not in the locker room afterward. Players were off Friday.

Late Friday, NFL Network reported that Martin sent a text to Incognito earlier in the day. In the text, according to the network, Martin said: “I don’t blame you guys at all. It’s just the culture around football and the locker room got to me a little.”

Reserve offensive lineman Nate Garner told the Palm Beach Post that any joking with Martin was “normal stuff.” Other players said it wasn’t anything that doesn’t go on in any locker room, but that Martin snapped.

Without acknowledging that anything improper had taken place, Philbin said, “This is something we take very seriously. It will not be tolerated.”

Martin, a second-year player, has struggled this season, although not as much as veteran offensive tackle Tyson Clabo. When the Dolphins acquired left tackle Bryant McKinnie on Oct. 21, Martin was moved from the left side to the right side and Clabo was benched.

Although some former Dolphins said it would be difficult for Martin to return because his teammates would see him as weak, Clabo said he would welcome Martin back.

“I want him to come back to work,” said Clabo, who started against the Bengals in Martin’s absence. “He’s a talented young football player.

“I can’t say what he’s feeling. I know if and when he wants to come back that I will be there to shake his hand.”

Garner also said he wants Martin back.

“He’s a great dude,” Garner said. “He’s a good ball player.”

Martin’s departure has received national attention. I Will Not Bully, a national anti-bullying organization, said it will monitor the situation. The organization Friday began following Martin, NFL commissioner Roger Goodell and the NFL Players Association on Twitter.

The organization’s executive director, Tamicia Currie, said she has not heard of bullying in pro sports. She was concerned about whether NFL players have a way to report concerns about harassment.

“Most people have a human resources department where you can go to report your grievances,” she said.

Dolphins spokesman Harvey Greene said “there are a variety of resources” available to players, including employee assistance programs. Kaleb Thornhill, Miami’s director of player engagement, is responsible for assisting players with off-field issues.

Currie said she regularly deals with bullying in youth sports. She said she wondered if it happens in pro sports but that victims are ashamed to discuss it.

“If I report I’ve been bullied, most people are going to be sympathetic,” she said. “Imagine you are an offensive tackle playing in the NFL. How are they going to view him? Publicly they may hold his hand, but privately scrutinize him.”