BBC Sport says a hamstring injury could see Fofana missed the remainder of the season.
Blues boss Enzo Maresca said: "Unfortunately he could be out for the season, so we don't know exactly for the entire season, but unfortunately he could be out for part of the season. And we are together here since we start, and every time you ask me about Wes, I said many times that I'm in love with Wes.
"I was in love with Wes, also because Wes is that kind of defender that gives you the chance to press and be aggressive and to leave him 1v1 with Watkins on pitch.
"We did exactly the same when Wes was injured with Benoit Badiashile, 1v1 with Solanke on pitch, and they can deal with that, and it's very difficult to find that kind of defender, but now unfortunately both are injured. We are trying to find different solutions, but for sure for us Wes is a huge loss."