Chelsea's goalscorer Hakim Ziyech was forced off with a shoulder injury during the Super Cup contest with Villarreal, causing Thomas Tuchel reason for concern ahead of their Premier League opener.
The former Ajax man had opened the scoring for the Blues in Belfast when he tucked in from Kai Havertz's cross in the 27th minute – Chelsea having dominated proceedings up until that point.
Ziyech, who scored twice in 23 Premier League appearances last season, had also created a game-leading four chances before he went down clutching his right shoulder in the 39th minute after helping to defend a Villarreal corner.
Chelsea's medical team rushed on to tend to the Morocco playmaker, providing him with an inhaler before Christian Pulisic was introduced in his place.
While the extent of his injury remains unclear at this moment, Tuchel would seem likely to be without Ziyech, who had to use his shirt as a makeshift sling as he walked off, for Chelsea's meeting with Crystal Palace on Saturday.
Ziyech returned from the dressing room with his arm in a sling as he took his spot behind the Chelsea bench for the second half. Villarreal's Alberto Moreno had struck the crossbar just before half-time, with the Blues still leading 1-0.