Jamie Carragher has slammed Mamadou Sakho after the Liverpool defender tested positive to a banned substance recently.

The French centre-half allegedly failed a drugs test prior to Liverpool's Europa League clash with Manchester United last month and is now facing a lengthy ban if his 'B' sample fails.

Anfield great Carragher cannot understand why modern professionals would go to the risky lengths of taking prohibited substances and believes Sakho has made a serious blunder that could have enormous repercussions.

"It's a nightmare for the player," former Liverpool star Carragher told Sky Sports News HQ.

"I think he's let himself and the club down badly, because he's become a really important player.

"There's serious questions to be asked of him.

"He's had a great campaign. He's one of the leaders of the team now, certainly within that run, thinking about how well he played in the Manchester United and Borussia Dortmund games. It's now how Liverpool fill that void.

"For a professional footballer, as in any sport, it's not acceptable."