The 21-year-old was inspirational as the Reds were held to a 1-1 draw against automatic-promotion-chasing North End but has now returned to Ewood Park.
The Championship side are low on numbers, with Rovers boss Gary Bowyer telling rovers.co.uk "Because of the numbers and how we are he will certainly be involved in the squad when he comes back."
Reds Head Coach Lee Johnson said after the draw, "I'm sad to see him go because I've enjoyed working with him. He's a good lad, really willing to work and improve - which I like. He asks a lot of questions, which is good. Hopefully, he'll go back and play for Blackburn."
O'Sullivan presented with the Man of the Match champagne by Palmer Construction Ltd
Dubliner O'Sullivan appeared eight times at Oakwell, with the Reds picking up six wins and two draws along the way - conceding just two goals.
The Club would like to thank John for his passion and effort during his loan spell here with the Reds and wish him the best of luck with his future career.
