Arsenal defender Kieren Tierney suffered a hamstring injury during Real Sociedad's 3-0 win against Athletic Bilbao on Friday.
After falling down in Mikel Arteta's pecking order last season, the Scotland international opted for a move away from the Emirates Stadium, joining Soceidad on loan until the end of the season.
But he may be ruled out for between 10-12 weeks, according to The Athletic, with the full-back being substituted after 25 minutes into the game against Bilbao.
It comes as a huge set-back in the 26-year-old's hopes of getting more game time with the Spanish outfit.