O’Brien blamed his lack of first team action on a clause in his contract, saying that a league appearance would mean Rovers had to give St Mirren an extra £300,000.
The youngster nearly broke into the first team under Brian Kidd, until he was sacked.
Chances have been limited since, and when Souness arrived it became apparent he had no future at Ewood.
Meanwhile 19-year-old ‘keeper Ryan Robinson has joined second division Wigan Athletic on a month’s trial.
Despite making it to the bench on several occasions last term, Robinson feels he has to find pastures new rather than sit behind Friedel, Kelly and Miller.