The former Salford Red Devils and Toronto Wolfpack player was deployed alongside Jake Trueman at half-back as the Tigers recorded a 52-16 victory over Leigh on Friday night.
However, O'Brien was substituted midway through the first half as he sustained an injury above his knee.
"He got a knock above his knee, so he will be a strong doubt for next week," revealed head coach Daryl Powell afterwards.
"We are not having much luck with half-backs at the moment. We put a combination out there but hardly ever finish with it.
"It is tough at the moment. Gaz has been great when he has been out on the field he has just been unlucky.
"We will just see how he is through the week."
Danny Richardson missed the fixture after aggravating a wrist injury in last week's Challenge Cup win over Hull KR.
Powell was unable to give a timescale on the half-back's return but doesn't expect the former St Helens player to be sidelined for long.
He added: "He has got a shoulder and a wrist injury, he came back last week with a wrist injury and made that a little bit worse.
"He is sore with his wrist, he is not massive with his timescales but we will have a look during the week and see."