After Sunday night’s win against Charlotte, Georgia Tech coach Brian Gregory almost sighed with anticipation at the challenge ahead with the opening of the newly expanded ACC schedule, and that’s before he knew what would happen with Robert Carter Jr.

What Tech thought was a “tweak” in the dynamic sophomore forward’s left knee turned out to be a meniscus tear. And on the eve of ACC play, which begins Saturday at Maryland, Gregory announced that Carter would undergo arthroscopic knee surgery and is out indefinitely.

Carter’s surgery is scheduled for Tuesday, the same day Tech will play at No. 7 Duke. The team won’t know until then the severity of the injury and how long he’ll be out.

“Some guys are able to come back, depending on how bad it is, in three to six weeks,” Gregory said Thursday. “Some guys, it’s three to six months.”

Carter had averaged nearly a double-double. He is tied for the ACC lead in rebounding with 9.3 per game and ranks fourth on the team in scoring with 10.3 points per game. He was a key force on offense and defense, giving Tech a versatile complement to Daniel Miller’s brawn in the low post.

Carter, a 6-foot-8 power forward from Thomasville, started each of his first 44 games at Tech.

“He’s a tough kid,” Gregory said. “And it hit pretty hard because he’s done a tremendous job for us this year. He has done everything that we’ve asked. He has changed his body. He’s more aggressive on the glass. I think his stats clearly show that he was having a tremendous sophomore season for us and is a big part of what we do both offensively and defensively.”

Carter injured his knee on a baseline spin move in the second half. He left the game, received treatment in the locker room and returned. But after a day off Monday, Carter still was in discomfort at Tuesday’s team shoot-around. An MRI later in the day revealed the tear.

“That definitely turned our world upside down a little bit,” said senior wing Jason Morris, whose role will expand to include some interior play. “But no one person is going to play hero. Everyone’s got to step up. Obviously with me at 6-6, 235, I’m going to have to go down there and play some (power forward). It comes with my size. Everyone is just going to pick it up. No responsibility has been put on one person to try and fill that giant void because Rob was an extremely important person for us.”

In the season and a half since Carter’s arrival, 6-8 Kammeon Holsey has been the sixth man off the bench, giving Tech another big post presence. He likely will start at power forward now and see his minutes increase.

“The positive, if there is one, is Kam has been more or less a starter for us the last two years,” Gregory said. “And so (you’re) bringing in a guy who’s a veteran. But there are going to be situations where we’re going to have different type of lineups in there. It’s a big challenge any time a team faces some adversity.”

Tech already has lost freshman point guard Travis Jorgenson for the season because of a torn ACL. He was expected to share ballhandling duties with Trae Golden, the senior transfer from Tennessee who now handles the bulk of them. The Yellow Jackets (9-4) are down to 10 healthy scholarship players.

“(Carter) is a big key to what we do, but it’s a long season,” Golden said. “Guys have just got to step up, and we all have big shoes to fill.”