Mitchell, who was regarded as the team's top receiver going into the 2013 season, underwent arthroscopic surgery after reinjuring his right knee running pass routes with teammates this week.
Quarterback Hutson Mason was working with Mitchell and didn't even realize he was hurt after he planted making a cut.
"The thing you want to pound your head over is it was the last route when it happened," Mason said Friday, shortly before the Bulldogs held their first practice of the preseason. "We were working on slant routes, slant routes, slant routes, and he just looked so explosive. He was looking so good."
Director of sports medicine Ron Courson said a full recovery was expected after Thursday's procedure but did not give a timetable for Mitchell's return.
The junior initially tore a ligament in his right knee in last season's opener against Clemson, knocking him out for the rest of the year. He then hurt his left leg during spring practice and missed the remaining workouts.
Mitchell had 40 catches for 572 yards and four touchdowns in 2012.
"There's no way to sugarcoat it," Mason said. "You're going to miss a guy like Malcolm. He's one of those guys you just find a way to get him the ball and let him do what he does best."
Coach Mark Richt said he is confident the Bulldogs can get by while Mitchell makes another recovery. Seniors Chris Conley and Michael Bennett have plenty of experience, sophomore Reggie Davis is coming off a promising debut season, and senior Jonathon Rumph has been a late bloomer in the passing game.
"We've got a lot of guys who have a pretty good feel about what we're doing and how to do it," Richt said. "We'll be fine."