"Regrettably I have been advised that a successful return to the pitch is unlikely and ultimately could lead to me having significant problems with my hand in the future," said Willis
"I have had a great time whilst with the Dragons and will always cherish memories of typical Newport Friday nights, fantastic Rodney Parade crowds and playing alongside a great bunch of guys.
"I'm very grateful and proud for the opportunity to be a Dragon and the support which everyone at the Dragons, and our regional fans have shown me over the past four years."
But Willis won't be a stranger at Rodney Parade as he plans to stay in Wales for the immediate future and continue his support of the region's developing hookers whilst of course continuing to support the team from the terraces.
"I firmly believe that the squad are heading in the right direction and that the future is bright for the Dragons. This is typified by the number of our boys presently in the Welsh setup.
"Darren and co are doing a fantastic job leading this team and by retaining the nucleus of the squad we can build on the foundations we have laid and bring some awesome rugby to Rodney Parade"
"I'd like take the opportunity to wish the team well for the rest of this season and for the future. Wherever I may be in the world, I will always keep a close eye on the fortunes of the Men of Gwent."
Dragons Head Coach Darren Edwards said, "We are really disappointed for Tom. His contribution to Rodney Parade should not be underestimated. He had been a key figure in changing the mindset and attitude of the team whilst helping our squad raise their ambitions.
"He has demonstrated an extraordinary work ethic and strong leadership at Rodney Parade and I have to say he is probably the most stand-up player I have ever worked with."