The former Warrington and Leigh utility back, who captained his country in last year’s World Cup, looks likely to return down under to pursue interests out the game.
Wilshere, 31, has played more than 70 games for the Reds in a three year spell, having spent a year each at Warrington and Leigh in Super League.
Football director Steve Simms said: “We offered John a new contract but he turned it down. We could not reach an agreement.
“It does now look as if John will possibly decide to return home to Australia at the end of the season.
“These things happen, an offer was made to him but nothing could be sorted out.”
Wilshere previously played a handful of games in the NRL for St George, Melbourne and Western Reds.