Ex-Wales and British & Irish Lions captain Gareth Thomas fears that former side Cardiff Blues are becoming one of the weakest teams in Europe.
The Welsh region have already lost three Pro12 games at home this season.
Then last weekend Blues let slip a 15-point lead to lose their Heineken Cup opener away to a Sale side that had lost all six games this season.
"If you go that far in front in... the Heineken Cup and you can't stay in front, it's really worrying," he said.
"Unfortunately, being an ex-Cardiff player and a Cardiff fan, at this moment in time after the Italian teams it's probably two of the weakest teams in Europe [Blues and Sale] coming up against each other.
"I thought if Cardiff could go there and - after the few disappointing defeats they've had in the league - win, it may have given them a bit of a boost.
"But to see them lose and also in the manner they lost when they were up, it was also kind of frightening because they're not really showing any maturity."
Thomas understands that Blues have been hurt by the financial problems afflicting Welsh regional rugby, which has seen the four regional sides impose a £3.5m salary cap.
With French clubs especially able to outbid for players' services, there has been a steady stream of leading Welsh players leaving to play their domestic rugby elsewhere.
"A lot of players left so it is kind of a transition, but to see one of the most famous clubs in the world - I know it's a region but... outside of Wales where people don't really recognise it as a region - in this run of form is massively disappointing," Thomas added.
"I really hope to be proved wrong, but they're playing Toulon on the weekend who are sitting top of the French 14... there's some twitching going on down there this week.
"The one thing I like about the Blues at the moment is they've got a lot of good youngsters: I'm a massive fan of Dan Fish, I think he's extremely creative, he's extremely exciting.
"But when you get to tournaments like this, the pedigree and experience you have as a player of being on the international stage or playing in top European games regularly stands you in good stead.
"That's my fear, that there are players in this [Blues] team that are very inexperienced at playing at the top level.
"Youth can take you a long way but there's no substitute for experience."