Mauricio Pochettino said he has received "bad news" about Chelsea defender Ben Chilwell's latest injury blow.
Chilwell underwent a scan on Thursday to determine the extent of the hamstring problem that forced him off in the closing stages of Chelsea's midweek League Cup win against Brighton.
Blues boss Pochettino confirmed it "looks a bad injury" although he was unable to put a timescale on Chilwell's absence.
After playing only 23 league games last season, it is another setback for the England left-back, who missed the 2022 World Cup due to injury.
"I think it is bad news from what the doctor told me. It is not a good thing," Pochettino told reporters on Friday.
"It looks a bad injury but we need to assess in the next few days and we will see the period he will be out.
"The mechanism was bad, in the last minute of the game. We are really sad about the news about Ben.
"It is difficult to know now, it is less than two days and we need to assess in the next few days."
With England right-back Reece James also sidelined, Pochettino admitted it was hard to replace to players of such high quality.
"At all clubs, important players are missed when they don't play," he said.
"If the question is 'do we miss them?' Of course. Reece is a top player and Chilwell also. When they're at their best, they are the best full-backs in the world.
Pochettino could be without as many as 11 players for Monday's west London derby at Fulham, with a lengthy injury list exacerbated by suspensions for Malo Gusto and striker Nicolas Jackson.
But when Pochettino was asked about Burnley boss Vincent Kompany's proposal that players should be limited in the number of games they can play in order to guard against injury, the Argentine said he was unsure if it was a realistic idea.
"Maybe there are players that cannot cope with 70 games during the season, but another player can cope with that," Pochettino said.
"Another player only can cope with a limited percentage, because the risk is massive to get injured again.
"It's difficult to generalise. We cannot put some limit on the players. The players want to play every single game. When it's a top player who wants to play, how do you say no?"
