Arsenal defender Gabriel was substituted in the 16th minute of their Premier League match at home to Fulham after picking up an injury.
The Brazilian centre-back, 27, went down after appearing to hurt his hamstring, before hobbling off to be replaced by Jakub Kiwior.
It is a potential blow to Mikel Arteta's side, who travel to Everton in the Premier League on Saturday, before hosting Real Madrid in the Champions League quarter-finals first leg on Tuesday.
The Gunners have been blighted by injury problems this season, with talisman Bukayo Saka returning to the squad for the match against Fulham after missing three months with a hamstring problem.