The 26-year old Belgian joined the Reds from Sunderland last summer and has been a key ingredient in their push towards the Premier League title.
"I've been delighted with Simon since he has come in," he told the Liverpool Echo.
"I think he's an outstanding goalkeeper who is only going to get better and better.
"He has come into a huge club and replaced a legendary figure at the club in Pepe Reina. That was always going to take a bit of time.
"But over the course of the season he has made a big contribution. I don't forget the significance of some of the saves he has made.
"Simon hasn't ever cost us a game but he has certainly gained us points. He's an excellent goalkeeper."
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