I suspect the medical team won't declare him in match worthy condition until the moment it's too late for him to go.
It can still change though, he's the captain, if he's fit he's going. Only reason he's not named is due to injury. Edit: he's not the captain, but I think he's still an important first team regular for them.
True that squads of 17 can be updated until January 7th but I doubt that Senegal would be prepared to risk a place in their squad for Diame given the strength of players that are definitely available.