Gareth Thomas made 100 Wales rugby union Test appearances
Gareth Thomas has undergone groin surgery in the hope he will return to fitness in time for Wales Rugby League's autumn campaign.
The Crusaders winger, 36, has made 13 appearances since his code switch in January, but the groin injury has kept him out for the last eight weeks.
He will also miss their crunch Super League clash against Hull Kingston Rovers Rovers on Saturday, 4 September.
Thomas wrote on Twitter: "Off to hospital for op first thing [Monday]."
He also posted: "Got Gilmores groin, which is a sports hernia, no wonder is wasn't getting better," adding: "I will 100% be fit for Wales first game... get ready to wear international jersey again."
Thomas later added in a statement: "I will have to miss the last game of the season against Hull which I am gutted about with the play-offs so close, but the operation had to be done as the injury was just not clearing."
Wales play two Italy friendlies in October, then defend their European Cup when they face Scotland, Ireland and France.
The winners of the European Cup will earn a place in the 2011 Four Nations against England, Australia and New Zealand.
Ex-Wales union skipper Thomas, who also captained the British & Irish Lions in New Zealand in 2005, is four months into an 18-month deal with the Crusaders, whose for a place in the eight-team Super League play-offs will be decided at the Racecourse on Saturday.
He has also played for Bridgend, Celtic Warriors and spent three years in France with Toulouse, where he won the 2005 Heineken Cup.
Wales' 51-man squad: Andy Bracek, Matt James (Barrow Raiders); Byron Smith (Batley Bulldogs); Craig Kopczack (Bradford Bulls); Mark Lennon (Burleigh Bears); Gareth Dean (Carcassonne); James Evans (Castleford Tigers); Chris Beasley, Ian Webster (Central Queensland Comets); Anthony Blackwood, Ben Flower, Chris Davies, Dafydd Carter, Elliot Kear, Gareth Thomas, Gil Dudson, Jack Pring, Jamie Murphy, Jordan James, Lee Williams, Lewis Mills, Lloyd White, Luke Dyer, Rhodri Lloyd (Crusaders); Ross Divorty (Featherstone Rovers); Matt Barron (Gateshead Thunder); Sean Penkywicz (Halifax); David Mills (Hull KR); Danny Jones (Keighley); Rhys Griffiths, Mark Wool (Leeds Met); Owain Brown (Leigh East); Neil Budworth (Mackay Cutters); Aled James, Andrew Gay, Ashley Bateman, Christiaan Roets, Geraint Davies, Joe Burke, Lewis Reece, Steve Parry (South Wales Scorpions); Jacob Emmitt (St Helens); Ian Watson, Phil Joseph (Swinton Lions); Ben Evans, Rhys Evans, Rhys Williams, Gavin Williams (Warrington Wolves); Ben Davies (Wigan Warriors); Matt Thomas (London Skolars); Mark Roberts (Unattached); Dale Blackmore (Rochdale Hornets); Liam Kennedy (Widnes Vikings Reserves).