The French midfielder has highlighted a potential weakness in his former Arsenal teammate's game as the two prepare to lock horns in the Champions League on Tuesday.
Flamini, who played alongside Fabregas at Arsenal, was full of praise for the Spain star's abilities but has hinted at a possible weakness in the 25-year-old's game which the Rossoneri could look to exploit.
"Fabregas is a player with many qualities, as he has incredible vision and is also very good in front of goal," he told Milan Channel. "As for his defects, at times he 'forgets' to defend."
Barcelona heads into the tie as clear favorite to progress, and Flamini conceded he would rather have faced a different opponent at this stage in the tournament.
"Barcelona have great individual talents and play wonderful football, so they are among the favorites for the trophy," he continued. "Admittedly, we would’ve preferred to face a different team at this stage, but they will certainly be two fantastic games. We will do everything possible to surprise Barcelona."