Tuchel says winger Callum Hudson-Odoi and wing-back Reece James are doubts for the trip to France.
"We will try to have them join in training later, but this will be a very tight race," said Tuchel.
Both players missed Chelsea's 1-0 win against Newcastle in the Premier League on Sunday.
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"As you know they were not involved and we will take the decision on those two after training," added Tuchel.
"It will be a very late call. First we need to weigh up the risk. Let's see after training if it is worth the risk or whether it is even possible first, as it will be a very, very tight race for them."
Chelsea take a 2-0 lead into Wednesday's second leg after goals from Kai Havertz and Christian Pulisic earned victory at Stamford Bridge.
The government has issued a special licence to allow the club to continue operating after freezing owner Roman Abramovich's assets, citing his links to Russian president Vladimir Putin.
As part of the licence terms, £500,000 can be spent on home matches but there is a £20,000 limit on away travel.
The average Premier League spend per away match comes in at about £30,000, and European away fixtures add an extra premium.
"It isn't about luxury and bling-bling," said Tuchel. "This is just a professional level of sports, where we play with two days between matches with our opponent having four days between matches and we arrive with the possibilities of injuries.
"For that, it is better to arrive with a plane rather than a bus. From my understanding, we have a framework to go and play in Lille with absolutely no excuses."
When asked if players would be willing to fund their own travel to avoid long bus journeys, forward Havertz added: "I would pay it, it's not a problem. That isn't a big deal.
"For us to come to the games is the most important thing. There are harder things in the world right now than if we have to take the bus or plane to an away game. I would pay, no problem.
"We are professionals and sometimes situations like this can happen. It's not easy for us, for the whole club and the fans. What we can do is to play good football and try to give the fans a smile in this situation."
Chelsea forward Kai Havertz says he would pay for travel to away games if required.
The club have been given a special licence to operate despite Roman Abramovich having his assets frozen by the UK government.
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