Dolphins halfback Sean O'Sullivan's mighty start to the NRL season has been halted, with the playmaker to miss up to 16 weeks with a pectoral injury.

O'Sullivan left the field in pain in Friday night's loss to the Broncos, before scans confirmed a ruptured pectoral.

He will miss between 12 and 16 weeks, meaning he will not return before the end of June at the earliest.

O'Sullivan's setback came after he was one of the shining lights of the start of the season, as the Dolphins won their first three game's before Friday night's loss.

Wayne Bennett's men suffered a double blow on Sunday, with in-form winger Tesi Niu to also miss at least four weeks after damaging a medial ligament in his knee.

The Dolphins did have better news with Kodi Nikorima, after he was cleared of a facial fracture and is in a race against the clock to recover from nasty cuts in time to face St George Illawarra on Saturday.

Jeremy Marshall-King (suspension) and Isaiya Kato (elbow) are in line to return against the Saints.