Justin Rose believes being overlooked for the 2010 Ryder Cup is behind Paul Casey's decision not to re-join the European Tour, making him ineligible for the biennial event at Hazeltine next year.
Casey gave up his European card ahead of 2015 and cited his decision to focus purely on the PGA Tour as the reason behind his climb back into the world's top 25.
The Englishman has opted not to re-join the European Tour next year despite only needing to play five events outside the majors and World Golf Championship tournaments to be eligible under new criteria.
Compatriot Rose has subsequently suggested that then captain Colin Montgomerie's decision not to select Casey as a wildcard for the 2010 Ryder Cup at Celtic Manor, despite being ranked seventh at the time, left him scarred.
"He's [Casey] a very, very good player and a great match-play player and I can only see him improving his world ranking," Rose said. "He's playing very solid golf and I expect Paul to have a big year next year.
"It could be another situation where he's in the top 10 in the world and not playing the Ryder Cup. I think obviously when Monty didn't pick him in 2010, I think that's left a bit of a scar.
"Maybe from that point of view, when you put so much into the Ryder Cup and feel like you should be on the team and you get let down like that, maybe that's harbouring some of his decision-making to this day."
European Tour chief executive Keith Pelley had hoped that lowering the number of events to maintain membership would convince Casey to re-join.
And Rose believes lowering the quota was a wise move, adding: "I think five tournaments, you can find those if you're willing for sure.
"I think the Ryder Cup is probably a big enough carrot where it warrants that, and Paul's a player that's going to be missed on the team. It's disappointing."