Justin Marshall has told the star-studded Ospreys they need to become mentally tougher and develop a ruthless streak to win major trophies.
The ex-All Blacks scrum-half made a shock move to Montpellier on Tuesday and says the Ospreys have players, skills and ideas to match the best.
But he added: "The players need to become mentally stronger and I think that's the one thing that's lacking.
"The mental attitude and ruthlessness to win is still not quite there."
Marshall's viewpoint will strike a chord with those who believe leading Welsh players often struggle to cope with criticism and the nation's high expectations.
But Marshall says embracing flak and living up to expectations is what drives New Zealand's mindset.
"There needs to be a balance between a great performance and a poor performance," he said.
"It's very evident in New Zealand rugby. New Zealanders have a pride in their performance and it's not just about winning, the performance is also at a level at which if it's unacceptable and they still win, then there's criticism.
"Sometimes as a player that's tough to take because you feel like you're always getting knocked even though you're winning.
"But that creates an attitude of absolute ruthlessness to win and to win with performance.
"There have been games the Ospreys have scraped when we've played rubbish - absolute rubbish - and I've been really annoyed in the changing room.
"But looking around the changing room the players would be slapping each other on the back, happy just to have won and mentally I found that a really difficult part of the game to overcome."
Marshall says the Ospreys' failure last season to beat Saracens in the Heineken Cup quarter-finals after comfortably beating them in the EDF Cup semi-final underlines his point.
He said: "I just don't think at the moment with the youth in the sides throughout the Celtic League - and in particular in Wales - that we have that cut-throat attitude and ruthlessness to win games, that win-at-all-costs attitude.
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"You can see that in Munster. They just go out there and play to win.
"Welsh teams need to develop that attitude, particularly at the Ospreys, because they can come off the back of good games and get too carried away and Saracens was a classic.
"We got too carried away with what sort of a team we were and how we rated them after the EDF Cup semi-final win.
"We came up against the same team in the Heineken Cup quarter-finals and they were more ruthless on the day and we thought we were better than we were and I hope we learned a valuable lesson from that day."
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