Harry Kane was forced off with an apparent ankle injury in Tottenham's Champions League quarter-final first leg against Manchester City.
The England striker appeared to turn his left ankle awkwardly in a challenge with City's Fabian Delph on the touchline shortly before the hour mark.
Kane was immediately helped down the tunnel by Spurs staff, unable to put any weight on the injury, as Lucas Moura came on to replace him.
The incident could be a huge blow not only to Spurs' hopes of reaching the semi-finals, but also their challenge to finish in the Premier League's top four this season.
Mauricio Pochettino's side host Huddersfield Town on Saturday before they face City away, just three days on from the second leg of the Champions League tie at the Etihad Stadium.