The 32-year-old, who had surgery two weeks ago, will miss a huge chunk of the RaboDirect PRO12 campaign and will also be absent for Leinster's entire pool three qualifying series as they look to defend their Heineken Cup crown.
Cullen said: "He was in yesterday. He only had surgery just under two weeks ago. I was surprised when I saw him because he has no neck brace or anything.
"He has a small scar on his neck. He's up and about, there are no issues. Obviously, he's just got to start back on the road to rehab.
"He's gone for surgery but he has carried that knock for quite a long time. You wouldn't necessarily see it when he plays but he has catered himself in training so he doesn't get another bang, doesn't get that 'stinger' sensation.
"His is a different problem, more stemming from his neck, obviously a disc fusion there. He looks great now after getting it done. I'm sure he'll be back."
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