The midfielder has been out since straining his hamstring ahead of the quarter-final second leg against Porto.
The Chelsea manager said: “Me personally, I think we can hope for Fulham, but don’t take it as medical advice.
“Maybe the physios and doctors will kill me for that. I think Madrid could be very close, but obviously he has not trained with the team.
“When should this happen? Tomorrow is the game, then we have two more days to prepare for Real Madrid for the semi-final of the Champions League. Hopefully Fulham is a realist target.”
Kovacic is the only injury concern for Chelsea.
Tuchel also confirmed Edouard Mendy would be back in goal after Kepa started the FA Cup semi-final against Manchester City, as well as the goalless draw with Brighton.
Chelsea XI: Mendy, Christensen, Thiago Silva, Rudiger, Azpilicueta, Kante, Jorginho, Chilwell, Mount, Pulisic, Werner
Subs: Arrizabalaga, Alonso, Abraham, Zouma, Hudson-Odoi, Ziyech, Gilmour, James, Havertz
Injury list: Kovacic
Doubt: Thiago Silva