Mossop, 25, has already had an extended lay-off due to his World Cup exploits, but decided the timing was right to undergo surgery on a two-year-old injury problem.
“In 2011 I suffered a shoulder injury which I have played on with for two years,” said Mossop.
“I could’ve quite easily played again this season without having surgery.
“But I spoke with (head coach) Brad Arthur and (football general manager) Daniel Anderson, and we all agreed that from my point of view, I wanted to come over and play to my full potential, which I thought was important.
“The big thing for me is I’m hoping to be at Parramatta for the long term, and I think now before I start it is better to get that fixed up so I can go into the season all guns blazing and hopefully give it my best shot.”