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The former Wrexham keeper praised the Irishman for putting in strong performances when called upon to deputise for Alisson Becker.
Addressing Carragher's comments in an interview with talkSPORT, Foster said: "I disagree… we've got some fantastic number ones in the Premier League, who are some of the best in the world.
We've been quite unlucky this season with a lot of goalkeepers getting injuries, and (clubs are) relying on number two goalkeepers to come in.
"The good thing for Liverpool, and it's probably the reason why they're still top of the league, is that their number two goalkeeper is Caoimhin Kelleher, who's been phenomenal.
"You can't really notice too much of a drop off from Alisson, but with the other teams, there’s a big drop off when their number two comes in."
Caoimhin Kelleher has been praised for his performances for Liverpool this season(Image: Getty Images)
Foster's endorsement for Kelleher is strong praise from a man who believes Alisson is still one of the best goalkeepers in the world.
His admiration for both Liverpool stoppers comes despite him placing Aston Villa's Emi Martinez at the very top of his list.
Speaking recently on his 'Fozcast' podcast, he said: "The two best goalies in the world right now are Alisson (Becker) and Emi Martinez, but Martinez for me is the best goalie in the world.
If I had to pick a goalie for any one game, I'd have Emi Martinez.
"Liverpool fans, please don't hate me for this because I think Alisson is the second best goalie in the world.
I'm not saying he's rubbish, but I’m saying Emi Martinez is probably just ahead of him at this moment in time."
Liverpool goalkeepers Alisson Becker and Caoimhin Kelleher
Foster has previously applauded former Liverpool boss Jurgen Klopp and goalkeeper coach John Achterberg for bringing Alisson to Anfield.
You're getting a guaranteed number one for the next five or ten years and it's worth every single penny.
"Then when it translates, and you get him through the door, and he hits the ground running and turns into one of the best goalkeepers in the world, it's a pat on the back."
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