Sydney Roosters have suffered a blow ahead of Monday night’s NRL local derby against South Sydney with skipper Braith Anasta ruled out with a back injury.

Anasta copped a knock during the club’s final training run and is set to be replaced by new signing Daniel Mortimer at five-eighth.

The injury has plagued Anasta throughout the off-season, keeping him out of all of the Roosters’ trial matches.

With Mortimer set to come into the starting side, back-up hooker Anthony Mitchell will likely start off the bench.