The Spanish defender has been a revelation at the west London side since Antonio Conte signed the wing-back in a £24m deal from Serie A side Fiorentina in the 2016 summer transfer window.
His performances over the past two and a half seasons were rewarded this week when Alonso put pen to paper on a new long-term deal with the FA Cup holders.
Sarri took over the reins of Chelsea FC in the summer and the former Napoli boss has reverted to an orthodox back four to result in Alonso being used at left-back.
The 27-year-old has struggled with more defensive responsibility alongside Cesar Azpilicueta, David Luiz and Antonio Rudiger at the centre of Chelsea FC’s defence.
Alonso was disappointing in Chelsea FC’s 2-2 draw with Manchester United at Stamford Bridge last weekend to suggest the Spain international has plenty of room to improve.
And Sarri, whose side remain unbeaten after nine Premier League games, remains confident that Alonso can become one of the top defenders in the world at Chelsea FC.
“I’m very happy for him. He can be the best left-back in Europe,” Sarri told his pre-match media conference ahead of Chelsea FC’s clash against BATE Borisov.
“He needs to improve in the defensive phase as he played in a five more, now he plays in a four. If he can improve he can be the best left-back in Europe.”
Alonso thrived on the left side of Conte’s defence with the license to push forward and support Chelsea FC’s attacking cast in their title-winning campaign under the former Juventus boss.
Indeed, the former Bolton and Sunderland defender scored six goals and made one assist in 32 appearances in the Premier League to help the Blues get their hands on the top-flight crown.
Alonso remained one of the Stamford Bridge outfit’s most consistent players throughout Conte’s difficult second season in charge of the west London side.
The Real Madrid youth product netted seven times and produced three assists to prove that he wasn’t a one-season wonder.
Chelsea FC will make the trip to Burnley in the Premier League on Sunday afternoon.
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