James Haskell's return from injury lasted less than a minute as the England flanker suffered a blow to head after entering the field in Wasps' 22-16 victory over Leicester Tigers at the Ricoh Arena.
Wasps survived an admirable second-half fightback from the Tigers, playing their first game since long-serving director of rugby Richard Cockerill was sacked, to record an 11th win from 13 Premiership matches and return to the top of the table at Saracens' expense.
However, as England coach Eddie Jones looked on ahead of his team's Six Nations opener next month, Haskell endured a miserable comeback in his first appearance since undergoing reconstructive surgery on an injured big toe last July.
Having been introduced in the 58th minute, the experienced forward got into an awkward position tackling Freddie Burns and crumpled to the floor in sickening fashion after banging his head on the hip of his opponent.
Haskell was forced from the field as a result, having seemingly been momentarily knocked out, but could be seen smiling on the bench following his mandatory head injury assessment.
As the game continued, Wasps director of rugby Dai Young told BT Sport: "He looks okay. Nothing too serious, hopefully."
Although Leicester - with head coach Aaron Mauger taking interim charge - were unable to record a morale-boosting win on Sunday, they could at least take plenty of heart from their response to trailing 19-0 inside half an hour.
Christian Wade, Tommy Taylor and Dan Robson went over as Wasps initially dominated, but the visitors came roaring back and got to within three points thanks to Peter Betham's try and two kicks apiece from Owen Williams - who was withdrawn with an arm injury - and Burns.
A 67th-minute Jimmy Gopperth penalty, after Dan Cole had been yellow carded for infringing at the breakdown, gave Wasps a welcome boost and Young's men held firm in the face of late pressure to move three points clear of Saracens at the Premiership summit.