Having missed six games courtesy of an ankle injury, Lukaku featured among the replacements for the Blues' Champions League meeting with Juventus earlier this week.
However, despite the Belgian having had several more days of training, Tuchel has effectively ruled out any chance of the 28-year-old starting against his former club on Sunday afternoon.
Speaking to reporters at a press conference, Tuchel said: "There is a bit of a difference between being ready for training and being ready for games. There's also a difference between being ready for games and Premier League games.
"The possibility that he starts is not very high. We cannot be sure what happens inbetween matches, and we have to find the balance between giving minutes and being absolute competitive for 90 minutes with the guys who start."
Lukaku has not featured for Chelsea since the European clash with Malmo on October 20. body check tags ::