Chelsea midfielder N'Golo Kante is likely to be out for up to three weeks with an adductor injury, says boss Frank Lampard.
The France World Cup winner suffered the injury during the 2-0 home defeat by Manchester United last Monday.
His absence is a setback for Chelsea, who have six league and cup games in the next three weeks.
"He has a muscle injury, similar to the one he picked up against Arsenal," said Lampard.
Kante's injury has come at a critical stage of the season for Chelsea.
Lampard's side entertain Bayern Munich in the last-16 of the Champions League next Tuesday before the return leg in Germany on 10 March.
Chelsea, who are fourth in the Premier League but without a win in four top-flight games, entertain fifth-placed Tottenham in a London derby on Saturday (12:30 GMT).
In addition, they host Liverpool in the fifth round of the FA Cup on 3 March, while they face Bournemouth (away) and Everton (home) in the Premier League on 29 February and 8 March respectively.
Kante, a Premier League winner with Leicester City in 2016 and Chelsea in 2017, has had several injury problems this season and has started 16 of his team's 26 league games.