Mexes has been out of action since sustaining knee ligament damage in April while playing for Roma.
The French defender joined AC Milan on a free transfer from Roma over the summer.
“It is great to be back out on the pitch again, playing a match,” Mexes told L’Equipe.
“I am happy and it is encouraging. I had some pain, but I believe I will feel pain for about a year. I was uncertain about making my comeback, but I feel good.
“I don’t think I will be able to play the next Serie A match against Juve. There is no need to rush.
“There is an international break coming up which means I will have two weeks off to work hard.
“Could I be recalled by the French team for the next set of qualifiers? Why not? If I am called upon I will go. I believe I am fit and I want to go, but I am short on matches.
“I believe I am still lacking in match sharpness. I mustn’t rush things. It would not be sensible for me to be called up. There are players with better levels of fitness than me.”
