Cullen hopeful O'Brien will make Six Nations

Sean O'Brien should be fit for the start of Ireland's RBS Six Nations campaign, Leinster head coach Leo Cullen has said.

O'Brien complained of tightness in his calf after Leinster's Guinness PRO12 win over Zebre two weeks ago and was forced to sit out last weekend's defeat of Montpellier.

It had been hoped that he would be available for the province's final European Champions Cup fixture against Castres on Friday evening, but the flanker remains sidelined.

With Ireland due to play Scotland in the Six Nations opener on February 4, O'Brien is in a race to prove his fitness to head coach Joe Schmidt but Cullen is hopeful that he will be fit for the start of the tournament.

"In the Zebre game didn’t feel an incident but when we came back in training that week [he] had a bit of awareness in his calf. We actually thought he’d be okay to play against Montpellier game that week. That was at the start of the week," Cullen explained.

“And it just probably hasn’t settled as quickly as we would have presumed so, yeah, it’s just like a mild strain, tear of his calf.

“You usually turn around those around quite quickly but it’s just been quite slow. That's why he misses out again this week."

The Leinster head coach added: “Those would not normally (last long) but I thought he would have been available this week it’s been a bit slower than we would have thought.

“I would have thought he would have turned it around for this week. It’s been a little bit slower. There is always a chance for complications with injuries even if they are very, very minor.

“I would imagine he would be fine for the start of the Six Nations. He was no a million miles off for this week but he’s not good enough to go this week.”

O'Brien picked up a serious hamstring injury against France in last year's Six Nations and did not play again until October.