Mason Mount became the latest injury concern for Chelsea manager Frank Lampard when he limped off in the early stages of the side's 1-0 defeat to Valencia on Tuesday night.
The 20-year-old has been a revelation so far this season, excelling at Stamford Bridge following a successful loan spell at Derby County last year.
He has scored in three of his first five Premier League games, establishing himself as a regular in the starting lineup, with his impressive displays earning him his first senior England cap earlier this month.
Mount was making his Champions League debut but his night was brought to a premature end following a heavy challenge from Francis Coquelin inside the opening ten minutes of the game.
The midfielder tried to continue, but was clearly struggling with an ankle problem, meaning that he had to be replaced in the 16th minute by Pedro.
Frank Lampard revealed the club will have to wait before discovering the severity of the injury, stating as quoted by BBC Sport: "We have to assess it over the next 24-48 hours to see the scale of the injury.
"We don't know how bad it is. It is an ankle injury and it is a shame. He's been playing so well and he started well tonight."
The extent of the injury is yet to be revealed, but it did not look good for Mount, with Football.London describing the youngster as "clearly emotional" when he left the field of play.
The setback comes ahead of an important game for Chelsea
Lampard has had to cope without N'Golo Kante and Antonio Rudiger
Source : 90min