Jonathan Davies believes the timing of Gareth Thomas' retirement suggests the 37-year-old felt the Four Nations Series was "a bridge too far".
Thomas was due to play for Wales' rugby league side against England in Leigh on Saturday.
Davies, though, feels Thomas has lost his hunger for the game.
"The timing would have surprised the Wales team management because they would have liked the decision a little bit earlier," he said.
After their opener against England, Wales then face games against Australia and New Zealand.
"Looking at the calibre of opposition Wales are about to play against, maybe he thought it was a bridge too far and that's why he made the call," said Davies, another dual-code international.
"But when you do retire it's a very, very tough decision to make because it's been your life for 10 or 20 years."
Thomas makes his exit from the rugby field having become the first Welshman to win 100 caps in rugby union.
The former Wales captain, in both codes, was also rumoured to be ready to extend his club career by signing for Wigan.
The season ended with Thomas leading the British and Irish Lions in New Zealand after original captain Brian O'Driscoll was injured in the opening Test.
"He's achieved most things that he set out to achieve," added Davies, a former Wales rugby union captain and Great Britain rugby league international.
"He played for the Lions, Wales, won the European Cup with Toulouse and then late in his career changed to rugby league. So a very full and eventful career.
"You don't survive for 100 caps without having passion for the game, and that's certainly what Gareth had.
"He was a very strong player, very fit, always knew where the tryline was."
Aged 35, Thomas made the shock decision to switch codes by joining Super League side Celtic Crusaders in 2009.
He made 31 appearances over two seasons, and won four caps for Wales, but Davies believes the switch came too late for Thomas to make a real impact.
"You need a little bit of time on your side to pick the game up and you need to go there at the peak of your powers," said Davies, who left union to join Widnes as a 26-year-old.
"Maybe Gareth had gone a little bit past that and the transition was very difficult. It was made harder by not going to one of the strongest Super League clubs.
"I think he did find it a little bit harder than maybe he thought."