The No.8 was forced off 28 minutes into Leinster's GUINNESS PRO12 encounter with Ulster at the start of January after picking up a shoulder injury.
The 31-year-old , who is rarely injured, returned to training this week and O'Connor revealed his captain would feature against French side Castres as GUINNESS PRO12 action makes way for European matters for the remainder of January.
"It's about a must-win game at home at the RDS," he told the Irish Examiner.
"You've got your best blokes available, you stick them on the field. Jamie's trained all week. He's done everything asked of him. Now he'll play.
"There's always going to be special athletes and freaks like Jamie. There's just not enough of them.
"In my time here, that AC injury is the first time he's missed a training session, and you very rarely get that in the game."
Heaslip himself admitted the experience of being sidelined had proved a strange one to him with 2010 being the last time he was forced off the field through injury.
But back fit again, he insisted he was ready and raring to go again as Leinster welcome Castres to the RDS Arena.
"I'm good to go. I'm like Benjamin Button, getting younger," he said. "The wolverine blood kicked in. It's been slightly embarrassing, being injured, it's been so long!
"The medics were laughing at me because they had to go back so far to look at my last scan from when I was injured in 2010. It's all on one page, I'm a one page man."
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