Former England striker Carroll and New Zealand defender Reid returned to London from a preseason training camp in Switzerland to undergo follow-up operations on injuries suffered last season.
“Andy played and scored in Sunday’s match (against FC Winterthur) but is still reporting some discomfort in his ankle and further scans have revealed that he requires some minor surgery to provide more strength and stability to the area,” Richard Collinge, head of the club’s medical department, said on the club website on Thursday.
“Winston has been suffering some swelling around the knee injury that he sustained at Swansea last season and he too is in need of explorative surgery to clean up the area.
“We have decided that this is the best course of action to ensure that both players have a chance of returning to full fitness as soon as possible.”
Manager Manuel Pellegrini said that in the absence of the senior pair, the club will look to add players to the five they have already signed in this offseason.