Mauricio Pochettino fears Harry Kane has suffered a season-ending ankle injury.
The Tottenham striker appeared to roll his ankle as he challenged Fabian Delph for the ball just after the hour of the 1-0 win over Man City in the Champions League.
Kane was carried straight down the tunnel and later left the stadium on crutches wearing a protective boot.
He missed a month of the season with ankle ligament damage in January and now his campaign could well be over.
"It is so painful," said manager Mauricio Pochettino. "We hope it is not a big issue and try to recover as soon as possible but it doesn't look good."
What Mauricio Pochettino said to Fabian Delph after role in Harry Kane injury
Asked if he was worried Kane's season could be over, Pochettino said: "Yes."
Pochettino felt Delph could have been sent off for the challenge but did absolve the City defender of blame for the injury.
He said: "I said to him, 'You were lucky'. Checking on the VAR, maybe technically it was a red card but I think both were fighting for a ball and had no intention to damage each other."
Dele Alli was also withdrawn late on after appearing to injure his wrist.
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Son Heung-min scored the only goal of the game for Spurs, who had skipper Hugo Lloris to thank for saving Sergio Aguero's controversial penalty.
"I am happy with the performance and the way we approached the game," said Pochettino, ahead of the second leg at the Etihad.
"We still have a lot of work to do. Manchester City are still the favourites to win the Champions League and it is going to be tough."
