Carter had surgery on Tuesday to repair a torn meniscus in his left knee.
Gregory said Carter will be evaluated over the next three weeks. The coach said the priority will be to protect Carter's future.
"There's a slight, very slight, possibility he might be able to play this year, but in my opinion we're going to err on the side of caution when we're dealing with a guy like Rob who has such a bright future," Gregory said.
Carter, a sophomore shares the Atlantic Coast Conference lead with his average of 9.3 rebounds per game. He is averaging 10.3 points per game.
Carter hurt his knee in a win at Charlotte on Dec. 29. The Yellow Jackets then lost ACC games at Maryland and Duke, each by double-digit margins.
Guard Trae Golden said Carter is optimistic he'll be back in about a month.
"That's not something I hold him to but he's a competitor, a tough guy," Golden said. "I asked him `How long do you think you're out?' He said four weeks. That's great. I know he's going to work to come back but we have to make sure he comes back 100 percent."
Gregory said Georgia Tech, which will play its ACC home opener against Notre Dame on Saturday, is still adjusting its playing rotation. Gregory is looking for ways to compensate for the sudden shortage of depth on the front line.
The good news for Georgia Tech (9-6, 0-2 ACC) is senior Kammeon Holsey, who was a starter in his first two seasons, is an experienced replacement for Carter in the lineup. Holsey had been the Yellow Jackets' sixth man, so freshman Quinton Stephens and others have to play bigger roles off the bench.
"It's a tough process," Holsey said. "Robert was averaging almost a double-double. He's a great player. It's tough but as a team I feel like we can do it."
It was no surprise the Yellow Jackets missed Carter's rebounding in their 79-57 loss at Duke on Tuesday night. Georgia Tech outrebounded its first 14 opponents before Duke claimed a 33-25 edge on the boards.
Senior center Daniel Miller had 14 points and eight rebounds, but no other Georgia Tech player had more than four rebounds. Holsey was held to two points and three rebounds in 18 minutes.
"It is important that we get back to the Georgia Tech style on the glass, and that's getting some offensive rebounds and making sure we control our defensive glass," Gregory said.
"You lose the ACC's leading rebounder and now it's everybody - it's not Daniel, it's not (Stephens) it's not Kam - it's everybody. We need our guards engaged and we need every tip-tap rebound."
Georgia Tech also is adjusting to another lineup change. Jason Morris, who had surgery on Oct. 14 to repair a stress fracture in his left foot, has replaced guard Chris Bolden in the lineup.
Morris has the size and versatility to play the two forward positions, so his role could change as Gregory looks for a new mix.
Gregory had good depth when Holsey rotated with Miller and Carter. Now the Yellow Jackets are left with smaller lineups when Miller or Holsey is out of the game.
"We're evolving," Gregory said. "I thought there were stretches, especially in that first half against Duke, we really offensively kind of figured some things out. The one thing is on the defensive end we don't have two big bodies protecting the rim like we have in the past. With Daniel and Rob in there and then Kam, those three guys were always fresh and we had great rim protection and that sometimes allowed us not to give as much help on the perimeter.
"That's going to change and so there's an evolution on both ends of the court that we need to get comfortable with."
http://accesswdun.com/article/2014/1/269726