The midfielder has suffered a hamstring injury.
"He’s been out for one week and I think he will now be out for two or three weeks more," Emery said of McGinn. "Our expectation is that he will be out for three or four weeks altogether."
"When someone is injured it is not good for the players and for us," he added. "But analysing his performances before he was injured he needed to improve and increase his performance levels. We were working with him on his focus.
"Now he is injured we must stay calm and work to recover as soon as possible - and hopefully we can work on the things he was not doing like he has been doing for the last two years. Trying to fit better into the system and getting better performances from him and the team when he comes back."