"Joey can go out there and be the best player," Megson told the Manchester Evening News. "He certainly has the potential and now he's got to go out and prove it both to himself and the club."
O'Brien, 22, finally appears to have put behind him the injury problems that have blighted his career. He missed the entire 2006-07 season with tendonitis in both knees.
And last season the elegant midfielder suffered repeatedly with hamstring problems.
"Joey trained really well in the close season. And since we returned he hasn't missed any training at all," added Megson. "He's done everything that's been required of him in his battle for fitness.
"I saw him when he was on loan at Sheffield Wednesday and he was terrific. He can play right-back or centre-half but I see him as a midfielder.
"He still has more to do but he has the potential to do that because he is good in the air, he can pass, he's got quality on the ball, good vision and a good physique. Now he's fully fit it could be a big season for him."