Arsenal left-back Kieran Tierney came off at West Ham with his right arm in a makeshift sling after sustaining a shoulder injury.
The north London club had already lost Hector Bellerin to injury in the warm-up, before Tierney was forced off after 29 minutes following a collision with Michail Antonio.
Arsenal fought back to win 3-1 with three goals in nine second-half minutes to end their nine-match winless streak.
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It was reported ahead of the game that Tierney's limited involvement in recent weeks was due to a secret shoulder injury.
Sead Kolasinac came on for Tierney while Bellerin was replaced in the starting XI by Ainsley Maitland-Niles.
Speaking after the victory at the London Stadium, interim head coach Freddie Ljungberg revealed that Tierney had been taken to hospital for a provisional check on a shoulder problem.
Regarding Bellerin, Ljungberg added: "He had a feeling in his hamstring in the warm-up and we took the decision. We weren't going to force anybody on if they didn't feel 100 per cent."
Granit Xhaka also came off injured, with Matteo Guendouzi coming on in his place after 86 minutes.
Arsenal signed Tierney from Celtic for £25m in August and has since made 11 appearances for the club.
Bellerin, meanwhile, returned from a knee injury earlier this season after nine months out. He has made 19 appearances this season.