The 22-year-old half-back has made seven appearances for Saints while on loan but is currently sidelined after being badly concussed in a match against Catalan Dragons a fortnight ago.
O'Brien has been left out of Saints coach Nathan Brown's team to play Wakefield on Sunday on the advice of the club's medical staff and will not be allowed to play against his parent club in Warrington's next match at Langtree Park on August 30.
The Wolves currently have both regular half-backs, Lee Briers and Richie Myler, on the injury list and coach Tony Smith was unhappy with the performance of makeshift pair Stefan Ratchford and Michael Monaghan in Thursday night's shock 16-6 home defeat by Widnes.
But Briers is expected to return for the trip to St Helens and O'Brien is likely to provide back-up during the play-off series.
"I don't think he's going to be directly needed to play but he'd be unlikely to play against us in the next match and it's unlikely that we'd head into a finals campaign without him as our back-up," Smith said.
"I've had some discussions with Nathan and Gaz about all that and we'll make a final decision."
Warrington also expect captain Adrian Morley back for their next game, while full-back Brett Hodgson has a fortnight to recover from the clattering he took from Widnes forward Hep Cahill.
Hodgson was carried from the field on a stretcher in the closing minutes of the first half after catching Cahill's arm across his face.
He was placed in a neck brace amid fears of a serious injury but Smith said: "He is fine.
"He has got some wear and tear on his nose - it was split. He has got stitches and like an L-shaped cut but he is fine in terms of everything else.
"He has got his wits about him and all the parts of his anatomy that should be working aside from his nose are working."