On Tuesday, Kai Havertz and Christian Pulisic scored in each half to give Chelsea a solid 2-0 first-leg victory over Lille, but the London club will be concerned about injuries to key players.
Havertz, the German forward who had already had two attempts on goal early in the game, sprinted down a Hakim Ziyech goal in the eighth minute, and the ball slid high off the field into the net.
After N'Golo Kante's quick turnaround and pinpoint pass, Chelsea left struggling striker Romelu Lukaku on the bench.
The game was a bit depressing as Lille sought to take something from the game into the second leg at home on March 16.
"They played excellent football and the first half was very difficult for us. Now it is halftime and the next game we need to win as well," Havertz said of BT Sport.
Chelsea kept Chelsea busy going forward with buzzing run from Renato Sanches, Benjamin Andre, and Jonathan Bamba.
The effort from all three players and from Jonathan David were either blocked, usually by defensive rock Thiago Silva, or slowed by Edouard Mendy in the Chelsea goal.
Chelsea, who will face Liverpool in the League Cup final on Sunday, may be satisfied with their two-goal lead, but they will be concerned about the fitness of pivotal midfielder Mateo Kovacic and of Ziyech, who both limped off early in the second half.
The club of Thomas Tuchel is on a slew of games this month, with games planned for five competitions.
The club world championship in Abu Dhabi was held ten days ago, but Ben Chilwell, Reece James, and Callum Hudson-Odoi were both paraded round the bridge.
Athletes also won games in the FA Cup and Premier League before Tuesday's game and Sunday's final at Wembley.
"We did not play our best football," Havertz said. "We could not get the aggressiveness of the last few weeks but we won 2-0, which is the most important thing. Sunday is another competition and we must focus on that right now."