The Spain international was a revelation in the 2016-17 and 2017-18 season under Antonio Conte after the Italian head coach signed Alonso from Fiorentina in a £21m deal in the 2016 summer transfer window.
Alonso proved an attacking influence at wing-back in Conte’s team as Chelsea FC used a 3-4-3 formation to allow the full-backs to push forward and support the attacking players with three centre-halves providing cover.
However, Sarri has switched back to an unorthodox four-man defence to leave Alonso with less cover at the back and the former Bolton star has been forced to adopt more defensive responsibility this term.
This tactical change has resulted in some uncertain performances from Alonso at left-back, playing a direct and indirect role in Manchester United’s two goals in a 2-2 draw with Chelsea FC at Stamford Bridge last month.
Former Liverpool FC defender Carragher believes Alonso needs to adopt a more defensive approach to ensure that aspect of his game is taken care of before venturing forward to support Chelsea FC’s attacking players.
“Going to left-back is not a massive difference but it is a difference,” Carragher told Sky Sports.
“You don’t have as much cover behind you. With three at the back, you don’t have that extra centre-back who comes across into that position.
“It was Gary Cahill who did a lot of that for him. Now it is David Luiz and if you actually look at the second goal that Manchester United scored to go 2-1 up, he got done by Juan Mata but if it had been a back three then Cahill would have been there to deal with that.
“I think David Luiz should have dealt with the situation better but the difference with being in a back four is that you need to be that little bit more switched on defensively.
“If you look at the game against Arsenal, he was caught out with the ball in behind him as well. These are the things that he needs to get better on.”
Alonso scored six goals and made three assists in 32 appearances in Chelsea FC’s title-winning season to prove a big at the west London outfit.
While some of his Blues team-mates struggled in the 2017-18 season, Alonso continued to thrive and netted nine times in the Premier League.
Alonso netted the winner in Chelsea FC’s 3-2 win over Arsenal at Stamford Bridge in their second league fixture of the season, while the Spanish defender has created more chances in open play than any other defender this season.
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news