Rabbitohs winger Alex Johnston says he will be racing the clock to be declared fit in time for Saturday night's Preliminary Final showdown with the Panthers, after a hip flexor issue forced him from the field early in the second half of last week's win over the Sharks. 

Johnston won't resume running until later in the week, and while confident he is making good progress, isn't certain he will be able to take the field. 

"It'll be touch and go to be honest. But I feel pretty confident the way it has recovered yesterday (Sunday) to today (Monday). On that trajectory I think it'll be alright," Johnston said. 

"I sort of knew when it happened it was a hip flexor thing. 

"I felt it but I still stayed out there for a while trying to see if I could do my job.

It got to a point there where I was like 'I think it's best to come off and someone can do the job better than me at the moment'.

Alex Johnston

"I will be doing everything I can just to get out there... [Monday and Tuesday] is a lot of physio for preparing to run and hopefully start running towards the end of the week."

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Should the prolific 27-year-old, who in Finals Week 1 scored his 30th try of the year to become the first player in Premiership history to achieve that mark in multiple seasons, be ruled out, former Panther Josh Mansour shapes as the likely replacement for coach Jason Demetriou.

Johnston hits 30

Mansour hasn't played an NRL game since Round 8 this year but has plenty of experience in big games, including winning a premiership with the Panthers in 2020 and playing three Origins for NSW in 2016.

Richie Kennar, who scored a hat-trick in his only game this season against the Knights in Round 17, is also listed among the reserves for the Rabbitohs.