The in-form 24-year-old left the field at Wembley holding his upper leg in the 87th minute after scoring twice in last Sunday's 4-1 win over Liverpool, and is now a major doubt for Saturday's Premier League lunchtime kick-off at Manchester United.
Worsening Manchester United's case, though, is that they're still wracked with injuries - Marouane Fellaini, Paul Pogba, Michael Carrick, Eric Bailly, and Marcos Rojo represent a huge chunk of their best midfield and defensive depth, and Zlatan Ibrahimovic is still out for awhile yet.
Second-place United and third-place Tottenham both have 20 points, five behind Manchester City after nine games.
Tottenham struggled without leading scorer Harry Kane, who missed the game with a hamstring injury, but nearly held out until United's sustained pressure told 10 minutes from the end.
Lukaku's head was crucial once more as he directed David De Gea's clearance into the path of substitute Martial, who sent his shot across Lloris and into the bottom corner.
"But I think the only team that had opportunities I think was us, apart from the Dele Alli chance, we controlled them very well". Asked about his gesture to the cameras, Mourinho said it had nothing to do with the Spurs bench or his counter-part Mauricio Pochettino and suggested it was aimed at his critics. "Don't speak too much, speak, speak, speak, relax". Don't be so nervous, relax.
"I think we had more chances to win the match, tactically hard for both teams, for both players".