South Sydney Rabbitohs flier Alex Johnston is in doubt for this weekend's clash with the Newcastle Knights with a reported quad injury.

A short turnaround won't be helping Johnston's cause, with the Rabbitohs having played last Saturday night in a win against the Parramatta Eels in adverse conditions, only to have to back up this Friday to play the Newcastle Knights.

It is reported that he has suffered an injury and is now racing the clock to line up for his team on Friday evening.

The injury news regarding their star winger, who has scored a staggering 16 tries in 15 games already this season, with 10 of those coming in his last 6 games, was the last thing South Sydney needed.

Missing Jai Arrow, Damien Cook and Cameron Murray to State of Origin, they have also been brought undone by a potential quadruple injury blow for Round 17.

While veteran Dolphins-bound prop Mark Nicholls is still a chance to play as he battles concussion protocols on the shortest possible turnaround to pass them, centre Campbell Graham, and forwards Hame Sele and Liam Knight have all suffered longer-term injuries.

Graham, who has been replaced by Taane Milne, has suffered a facial fracture which could keep him out for up to six weeks on the run to the finals, while Sele has suffered a groin injury which will see him sidelined for between four and six weeks.

Knight, who hasn't been playing first grade in recent weeks, could have been called up this week given the number of outs, but had his season brought to an end by a cannonball tackle in the NSW Cup last week, with an ACL injury set to see him sidelined for virtually all of next year's pre-season.

Should Johnston be out, then it's tipped Richard Kennar would come into the side after he made the 22-man squad yesterday. Michael Chee-Kam could be another option to play in the centres after being named on the bench, with Milne pushing out to the wing.

The other reserves - one of whom could come onto the bench if Chee-Kam starts - are halfback Dean Hawkins, and forwards Shaquai Mitchell, Ben Lovett, as well as recent signing Daniel Suluka-Fifita.