Craig Clarke (right) and Liam Messam led the Chiefs to back-to-back Super Rugby titles © Getty Images

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The debate over the effect of concussion on players once more took centre stage with the news that Craig Clarke has been forced to retire with concussion issues after just 15 games for his Irish club Connacht.

Clarke, 30, has not played since he suffered his 10th concussion in 22 months in a Heineken Cup loss to Saracens in January.

"While it is of course extremely disappointing the way my career has come to an unexpected end, I am, at the same time, so thankful for the opportunities afforded to me through my involvement in the professional game," Clarke said. "I am proud of what I have achieved. I have experienced tough times with teams, which has just made me appreciate the good times all the more.

"While I will always be disappointed not to have worn the black jersey of my country, I will sleep easy knowing that I gave it a real crack, particularly in my last three seasons playing in New Zealand."

All the best to Craig Clarke on his forced retirement from rugby today @connachtrugby @ConnachtClan @IrishRugby pic.twitter.com/a7RFk0me2i

— Inpho Photography (@Inphosports) June 3, 2014

Clarke left for Ireland after leading the Chiefs to back-to-back Super Rugby titles in 2012 and 2013. He was the co-captain with All Blacks flanker Liam Messam. He joined Connacht on a three-year deal.

"I understand that health takes priority over sport every time, but I still can't escape the disappointment that I couldn't contribute to Connacht Rugby as I would have liked and envisaged before my arrival," he said.

Clarke, his wife, Veree, and daughter, Isabella, will return to New Zealand to work on their farm and he is "excited about the prospect of getting into coaching at any level and continuing my involvement in the game".

Connacht team manager Tim Allnutt said: "Craig was obviously one of the biggest signings we've ever had at Connacht and it was huge for us to get someone of his experience. But he also had all the qualities of a Connacht team man and we are extremely disappointed for him that his time with the club has been cut short. As is the case with every player, the priority is his health and we're thankful that every precaution has been taken here."

Connacht coach Pat Lam said Clarke's "work ethic and attitude was inspirational and he had a major influence, leaving a lasting impression on the squad".