"That means he's unable to play any part in the Test series, so he's flying home."
Onions is with England already, having been added as cover because of what were thought minor injury concerns hanging over Bresnan among others. The Durham seamer will therefore be officially added to the squad. England must nonetheless rethink their gameplan, in the absence of first-choice seamer Bresnan.
Strauss added: "We're all gutted for him, because it's come from left-field. It's surprised him and us."
The captain reported mixed news on England's other injury niggles.
Graeme Swann, who did not take the field today because of tightness in a leg muscle, is to be sent to hospital for a precautionary scan.
Strauss is confident the off-spinner's condition is not too much cause for concern, however.
Fast bowler Chris Tremlett, ruled out of the opening tour match because of an eye infection, is to see the doctor tonight.
But wicketkeeper Matt Prior, who bruised the ring finger of his left hand on the day before this first fixture, will be fit to play in the second against a PCB XI at the same GCA ground venue on Wednesday.