Jose Mourinho fears Harry Kane will be absent for a "few weeks" after suffering two separate ankle injuries during Tottenham's 3-1 defeat to Liverpool.
The Spurs captain was substituted at half-time after twice requiring on-field treatment.
After hobbling away from a challenge by Thiago, Kane then suffered another knock when he tangled with Jordan Henderson.
Save over 25% with NOW TV
Catch Arsenal vs Man Utd on Sky Sports for just £25 p/m for 4 months (usually £33.99 p/m)
"He is injured in both ankles and he says that to cope with one pain, he probably could, but he says with both, it is very painful, very sore and both ankles are getting big in both feet," Mourinho told BT Sport.
"He couldn't [carry on]. He is a guy with a good sacrifice spirit, he can fight against pain, but it was difficult for him."
Although Mourinho told the BBC that Kane would be ruled out for "a few weeks", he subsequently added in his post-match press conference: "You know, for Harry to leave a game, when he wants to play always and with the team losing, it is not a nothing injury. For how long I cannot tell you, I don't know, we have to wait and see."
Kane was replaced by Erik Lamela at the break at the Tottenham Hotspur Stadium, with Spurs going on to concede two second-half goals from Trent Alexander-Arnold and Sadio Mane as they missed the chance to move fourth in the Premier League.
The England captain missed nine games of Tottenham's campaign last season after suffering a serious hamstring injury against Southampton on New Year's Day, but has started all 19 of their Premier League games this season, with back-up loan arrival Carlos Vinicius given only 24 minutes of league football to date.
England manager Gareth Southgate will be concerned over the prognosis of his talisman, with their World Cup 2022 qualifiers getting underway against San Marino at Wembley in less than two months, on March 25.
In pictures: How Kane's problems unfolded
Pitch to Post Preview - Arsenal v Man Utd build-up, plus: Man City's title charge, Liverpool's return to form, and problems for Tottenham
In this week's Pitch to Post Preview Podcast Sky Sports pundit Jamie Redknapp joins Peter Smith to look ahead to the big Saturday night clash between Arsenal and Manchester United, and gives his verdict on Emile Smith Rowe, Martin Odegaard - and why Man Utd slipped up against Sheffield United.
We also get the inside story on Man City's title pursuit from Sky Sports News reporter Ben Ransom, who explains how one City star has been transformed by Pep Guardiola's methods this season.
And Sky Sports feature writer Adam Bate reflects on Liverpool's much-needed win at Tottenham - and the injuries sustained which could impact both sides. Plus he makes his Pitch for what will happen in the next round of Premier League games…