Tottenham manager Andre Villas-Boas hopes he will not be without Mousa Dembele for too long after revealing the midfielder has suffered a recurrence of the niggling hip injury which sidelined him for Fulham last season.
Spurs greatly missed Dembele's calmness and distribution on Saturday as their four-match winning streak came to an end at the hands of Chelsea, who ran out 4-2 winners at White Hart Lane.
Dembele, 25, who has been a big hit since arriving for £15million on deadline day, had to come off at half-time during Belgium's win over Scotland on Tuesday after triggering an old hip injury he suffered at Fulham last season.
The versatile player missed three games towards the end of January with the same problem and Villas-Boas admits losing Dembele for a similar length of time would be a big blow for the Londoners.
"Top players are missed," Villas-Boas said. "He had a scan, but we haven't seen the results yet. He suffers discomfort and pain on his hip which is not something that shows on the scan so it's difficult to assess.
"Fulham took him off for a period of two weeks. He had a chance to play (on Saturday) and had a late fitness test but the pain didn't go away.
"It's something that comes back to him. He fell awkwardly in the Scotland game against Belgium and felt the pain."
Without Dembele and Gareth Bale - who missed the game because his partner went into labour - Spurs looked weak in midfield, with Tom Huddlestone still lacking match sharpness after recovering from a long-term ankle injury this summer.
Much had been made of Villas-Boas' hidden determination to get one over on his old employers and defender Jan Vertonghen admits the manner of the derby defeat was frustrating.
The victory over Aston Villa aside, Spurs have failed to produce a solid 90-minute display at White Hart Lane this season.
Only a much-improved second-half display allowed them to beat QPR and the team were patchy at best against West Brom and Norwich, while they were terrible in the first half against Chelsea, who should have had more than a Gary Cahill goal to show for their dominance.
"At home we seem to play better in the second half than the first," said Vertonghen, who signed from Ajax this summer. "We need to think about how to put two strong halves together.
"We need to work out how to put a bit more pressure on teams from the start.
"They were the best team I faced this year, but I knew they would be. I knew their players before I came here and what they are capable of. Chelsea are a good team but I feel we should have done better."