The 27-year-old expected to be stuck on the treatment table for the rest of the season but admits he is now hoping to be back on the training pitch within a fortnight.
But O'Brien knows there is plenty of work to be done to make that dream a reality - and to regain his Ireland shirt from Chris Henry ahead of the summer.
"It's going very well. I'm back ahead of schedule and I'm just looking forward to starting my pre-season in two weeks' time," he told KCLR FM.
"That'll be tough work for six or eight weeks, but it's something I'm looking forward to.
"I'm just looking forward to getting fit again and getting cracking into the year when I do get going.
"We are after taking a step forward and we're playing a good brand of rugby. There's exciting times ahead I think.
"There is massive competition there in the back-row now and Chris had a great tournament, so fair play to him.
"I'll have to fight for my place when I get back and I look forward to that."
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