Arsenal are assessing a back injury to new signing Kim Kallstrom, Press Association Sport understands.
The 31-year-old midfielder moved to the Emirates Stadium on a loan deal until the end of the season on Friday and his arrival was the only incoming business concluded by the Gunners during the transfer window.
Reports in Sweden on Saturday morning suggested the former Lyon man had suffered a long-term injury during his first training session, claiming he could miss a large part of his temporary stay at Arsenal.
But it appears the seriousness of Kallstrom's injury is yet to be determined by the club, who will be hoping to have him available as soon as possible with fellow midfielders Jack Wilshere and Aaron Ramsey also injured and Mathieu Flamini serving a four-game ban.
Arsene Wenger's side enter an important month in their search for silverware and, after a home game against Crystal Palace on Saturday, face a daunting schedule including Premier League and FA Cup tussles with Liverpool, a league visit from Manchester United and the opening leg of their Champions League tie against holders Bayern Munich.