Ireland flanker Sean O’Brien is set to undergo surgery in the UK and has been ruled out of the summer tour to South Africa and the rest of Leinster's season.

Ahead of their Guinness Pro12 semi-final with Ulster at the RDS tomorrow night (KO 7.45pm), Leinster head coach Leo Cullen has confirmed the abrasive flanker will see a specialist over his hamstring injury and no return to play date has been put in place.

The Carlow native will travel to the UK tomorrow for surgery and has played just six games for his province this season, completing 80 minutes on just two occasions.

O'Brien signed a three-year contract with the IRFU last December which will keep him at his native province until after the 2019 Rugby World Cup.

"Sean's seeing a specialist in the UK tomorrow so he's more than likely going to have to have surgery," Cullen told RTÉ Sport.

"So he'll be out for the rest of the season and we'll see after that when we get a proper report post his procedure.

"It's frustrating for Seany but hopefully he gets sorted now and has a good clear plan in place that gets him back playing.

Cian Healy is unlikely to feature for the rest of the season either as he is troubled by a knee issue, but Leinster remain hopeful Rob Kearney will be available if they make the Pro12 final.

The full-back has been troubled by an ankle injury but returned to running at training today.

"He (Kearney) was just back running today. It was good to have him involved," said Cullen.

"He got injured against Treviso so he's only just starting his return to play. That should make him available for our next game, whenever that may be.

"Cian's had a couple of issues ongoing. He's pretty unlikely to play again this season.

"He's had an issue with a nerve from his neck, a procedure he had done last season, and a thing with his knee as well. He's making good progress and hopefully we'll see him at the start of next season."