Signed last summer, the Georgia goalkeeper will leave Valencia for Liverpool at the end of the season.
“I was very surprised when Liverpool bought Mamardashvili,” Westerveld told the Liverpool Echo. “I know this guy. I follow the Spanish league and I know how good he is.
“I said it on television in Holland after the Euros. I think he was the best goalkeeper at the Euros, so I know how good he is.
“I'm not worried but it's a little bit strange that since the moment he signed for Liverpool, his level dropped in Spain, and there's been criticism of him or maybe he will be dropped.”
Westerveld also said: "So I think you should have a number one and a really good backup. You can have a very experienced one who knows he's the number two, so he can come in and then he doesn't need to play five games to really play. With his experience, he can come in.
“Or you have a youngster like (Caiomhin) Kelleher, who comes in and shows himself and the quality. At the moment we're having a luxury problem, I think at Liverpool and hopefully we have that next season as well.”