The hooker did not play for Leinster in their Champions Cup match against Montpellier last weekend after sustaining an injury to his hamstring during the province’s convincing victory over Zebre two weeks ago. 

Since then, a scan revealed the severity of the injury which will require ten weeks of rest, meaning the 30-year-old is not expected to return to the game until the end of March. 

Cronin will be watching from the sideline when Ireland get their Six Nations campaign underway against Scotland at Murrayfield on February 4 and is unlikely to be ready for Leinster’s Champions Cup quarter-final on the first weekend in April.

“It’s quite a significant hamstring injury,” assistant coach Stuart Lancaster told The42.ie.

“It’s a real shame for him as he’s actually playing great rugby but it’s a good opportunity for us to get him right and make sure we don’t get a recurrence of this because it must be hugely frustrating for him.

 “He’s got himself into great form and now he’ll miss the Six Nations. He went to push off and accelerate around the corner and saw it go. He’s deeply disappointed but he’ll be back a better player.”

The injury will almost certainly impact Cronin’s chances of Lions selection. Hooker is already one of the most hotly-contested positions, with the likes of Rory Best, Dylan Hartley and Jamie George in the running, and Cronin will now have no international game time before the tour begins. 

Luckily, Ireland head coach Joe Schmidt has several choices for the hooker’s replacement. Cronin’s absence could mean international honours for previously uncapped Niall Scannell or Dave Heffernan.

Alternatively, it may give fellow Leinster hooker James Tracy an opportunity to build on the one international cap he has gained so far.