Arsenal medical staff are unhappy with Per Mertesacker's stand against taking drugs.
The Daily Mail says Mertesacker has been missing due to a chest infection.
The German's apprehension at taking antibiotics to clear up the illness is understood to have perplexed members of the staff at the club's London Colney HQ.
Gabriel has stepped in for Mertesacker and impressed manager Arsene Wenger during the German's absence.