Lukaku made a cameo off the bench against Manchester United last Sunday, having picked up the injury against Zenit Saint Petersburg in the Champions League in October.
The 28-year-old has scored four goals in 12 appearances across all competitions since joining from Inter Milan in the summer but had gone seven matches without a goal prior to his injury.
Lukaku could start for Chelsea against Watford in the Premier League on Wednesday, and Tuchel is confident he can regain his best form when given time.
"We showed with him and we showed without him that we're capable of scoring and capable of winning," Tuchel said.
"I think it's a process of adapting in both ways; the team will adapt to him and he will adapt to the team.
"The most important thing is that he becomes fit and gains fitness and a physical level that he can start for us. The rest, I'm pretty sure will take care of itself.
"I'm absolutely convinced and have zero doubts that he will have a huge impact on our team once he's back.
"He's pushing every single day and pushing everybody to try to be out on the pitch again. He tries to convince us that he's ready to start.
"We gave him some minutes [against Man United], which helps him psychologically and this is very important, but he is determined and trains on a very high level.
"Once we have the opinion that he's fully fit, I think he's ready to go and contribute what he can, which is a lot.
"We still believe that he can make the difference for us but at the same time, we will be patient."
