Graham Potter fears for the fitness of Ben Chilwell after the Chelsea full-back limped off against Dinamo Zagreb, just 19 days before England start their World Cup campaign.
Denis Zakaria scored what proved to be the winner just 30 minutes into his Chelsea debut after Raheem Sterling had cancelled out Bruno Petkovic's seventh-minute opener on Wednesday.
Chelsea congratulated one another with muted celebrations at the final whistle, though, after Chilwell was helped off the Stamford Bridge pitch by the Blues medical team following a hamstring injury.
Head coach Potter conceded the left-back's injury looks "not great" and leaves both Chelsea and England concerned over the left-back's fitness.
"Not great, he pulled up like that when he turned – not positive at the moment," Potter said of Chilwell's injury after the 2-1 Champions League win.
"It's a blow for us after an otherwise positive game, to see him pull up like that is not a great sight.
"Fingers crossed when we get it scanned it isn't as bad, it can be not as severe, but clearly we are disappointed."
Potter became the first Chelsea boss since Roberto Di Matteo, who won the competition in the 2011-12 season, to go unbeaten in his first five Champions League games in charge.
The Blues had already secured progression to the knockout stages as Group E winners, but delivered a performance that matched Potter's expectations in their final group game.
"I'm really pleased to get the win. I thought Denis was really good, he played with enthusiasm, he got forward and I'm really pleased with him. It was a great debut," Potter told BT Sport.
"The worry would be if you're not creating the chances. Our intent was good, our play was good and the quality was there from the players.
"We got a win, we got a performance. We're a work in progress but we can be pleased with our Champions League performance."
Zakaria became the 15th player to score on his Champions League debut for Chelsea, with what was his first attempt for the club, though he was made to wait for his chance for the Blues after joining on loan from Juventus in the last transfer window.
"Very, very difficult I have to say. I like to play and always want to play," Zakaria told BT Sport when asked about the wait for his debut.
"When you have to see your team-mates from the bench it is not easy but I was always behind the team and was waiting for my chance. Today it came and I took my chance."
Chelsea host Arsenal in Sunday's crunch Premier League clash and Zakaria hopes an impressive debut will work him another start, adding: "I hope so but I think that is a question you will have to ask the coach!"