Rajon Rondo vowed to return this season, but the Boston Celtics' star point guard is still struggling to get into game shape as part of his final preparations for his much-awaited comeback.

According to ESPN, Rondo admitted that getting back into game shape has been the biggest hurdle for him in his rehabilitation following an 11-month layoff due to an ACL injury.

Rondo, who sustained a partial ACL tear in January, has been spending extra conditioning sessions and pick-up games with teammates after their regular practices to improve his conditioning.

While he has made progress as proven by his ability to dunk off his left leg in their recent practices, Celtics coach Brad Stevens said that Rondo is still far from being in top form, saying that the seven-year veteran playmaker was "huffing and puffing" after one of the drills during their recent practice.

Stevens added that Rondo's struggles are normal after not playing for 11 months, but he expressed concern that their schedule would limit Rondo's opportunities to practice with team and to experience real-game scenarios that could help him in his comeback bid.

"How do you get to be game-conditioned without a lot of game opportunity or without a lot of practice opportunity, and real game-like scenarios? We tried just a quick little drill at the end to help him with that a little bit and he was huffing and puffing. But that's part of it. That's part of why we did it, and especially after three days off." Stevens said.

Stevens pointed out that for Rondo to get at least near his ideal shape, the 27-year-old All-Star point guard will have to work on his own because he can't force his other players to train with Rondo during their breaks.

"I think a lot of that's going to have to be on his own," Stevens said. "Again, that's not atypical. We can do a little bit more, but you can't wear your other guys down because it's a long season for everybody."

Rondo's return will not only renew the interest of Celtics fans towards their rebuilding team, but also the interest of other teams, who are looking to trade for the superstar point guard.

Rondo will become a free agent in 2015, fueling speculations that he could force his way out of Boston before he becomes a free agent.

Recent rumors suggested that the New York Knicks will look to trade for him, but Celtics president of basketball operation Danny Ainge has insisted that Rondo will not be traded.