The Chilean was granted an extended break following his involvement in Chile’s Confederations Cup campaign earlier this summer, with the final of the tournament taking place on July 2.
Wenger confirmed this week that both Sanchez and Mustafi, who also played in the tournament, would return to training on Sunday.
However, Sanchez’s participation has now been thrown into doubt after the 28-year-old took to social media to share a photo of him and his faithful pooch with the caption ‘sick’.
The former Udinese man can be seen wearing a scarf indoors and is claiming to have been laid low by a virus.
Sanchez has been a popular topic of conversation in recent week, with the player moving in to the last 12 months of his contract.
The Arsenal forward is believed to be keen to leave the club this summer as he looks to play Champions League football but Arsene Wenger insists that there has been no transfer request from the player.
The Frenchman stated last week that Arsenal’s decision was ‘not to sell’ Sanchez this summer, despite his contractual situation.