South Sydney has suffered a major blow in the lead-up to the start of the National Rugby League season, with promising young prop Scott Geddes ruled out for the season.

Geddes, 22, will undergo MRI scans on his right knee on Monday but club doctor Andrew McDonald said he was certain to require a season-ending knee reconstruction.

The Moss Vale junior twisted the knee while being tackled after 25 minutes in a Premier Division match in the curtain-raiser to the Charity Shield clash between Souths and St George Illawarra at Aussie Stadium.

Geddes was prevented from playing in the main game because he still had to serve out a two-match suspension incurred last season.

He said he felt shattered after being earmarked by NSW coach Phil Gould as a certainty for selection in the Blues' 30-man Origin squad, which will gather together on April 14.

"I'm pretty devastated about it," Geddes told AAP.

"It's funny how quick things turn around. One week everything's going good for you and the next week you get that (the injury).

"I've just started to make a bit of a name for myself and I was hoping to play a bit of good footy. It's pretty hard to take."

Geddes said he felt his knee dislocate but he didn't think it was too serious.

"It was pretty embarrassing getting carted off in that little medi-cab," he said.

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