The 31-year-old player is currently one of the longest serving players in the Chelsea squad, having joined the Blues in 2016 from Fiorentina.
Alonso signed for a fee in the region of €24 million. He helped the London side win the 2016-2017 Premier League title under Antonio Conte's regime.
The Spaniard has remained a consistent player at Chelsea, finding regular playing time under every manager at Stamford Bridge.
Alonso has also been a versatile player for the Blues, playing both as a left-back and also as a left-wing-back. He has also scored the most goals by any defender in the league since joining in 2016, with 25 league goals to his name.
Should Alonso eventually leave Chelsea this summer, there will be a huge vacuum at the left-back position. However, the Blues will definitely be in the market to find a suitable replacement for the 31-year-old star.
This article will thus be taking a look at some players who could be considered to replace the Spanish defender.
#5 Nicolás Tagliafico (Ajax)
One player who could be a decent replacement for Alonso will be Ajax defender Tagliafico, who has been linked with Chelsea in the past.
Sports Illustrated reported in January that the Blues had considered making a move for the left-back in a bid to provide back-up for the injured Ben Chilwell.
Tagliafico has a contract with Ajax until the summer of 2023 which could present an opportunity for the Blues to table a sizable bid.
He is a highly-rated left-back who can defend as well as score and cross. The Argentine has played 30 games for Ajax, scoring three goals and helping his team keep 18 cleansheets in all competitions.
#4 Marc Cucurella (Brighton)
Another player who could be considered by the Blues in terms of replacing Alonso this summer is fellow Spanish defender Cucurella.
The 23-year-old star has been one of the revelations of the season, putting on impressive performances for his side Brighton & Hove Albion in the League.
Cucurella is believed to be on Chelsea's transfer radar this summer and is also attracting transfer interest from Manchester City. The Blues could decide to rival Pep Guardiola's team for Cucurella's signature, as he would no doubt be a good addition to their team.
The Spanish left-back has played 38 times for Brighton this season across all competitions, scoring once and helping his team keep 10 cleansheets in all competitions.
#3 Borna Sosa (VFB Stuttgart)
Another decent replacement for Alonso at Chelsea is highly-rated Bundesliga and Croatian defender Sosa, who has been outstanding for VFB Stuttgart.
The 24-year-old left-back is reported to be attracting transfer interest from the Blues, according to Sports Illustrated. As he can fill any possible vacuum should Alsono depart this summer.
The Croatian defender is a specialist at crossing the ball and finding a teammate in the box. This could prove to be very useful for the Chelsea forwards considering how football is evolving around full-backs.
Sosa has made a combined total of 30 appearances for VFB Stuttgart this season, scoring two goals and providing nine assists in all competitions.
#2 Ian Maatsen
The Blues could as well turn to their very own academy graduate Maatsen to step up and replace Alonso next season.
The 20-year-old defender is highly-rated at his parent club Chelsea. He could be given an opportunity to impress head coach Thomas Tuchel once he returns from his loan spell at Coventry City.
Maatsen could save the Blues a lot of money in the transfer market this summer. He could be a decent option at left-back, and could learn a lot from Ben Chilwell in the process.
The Dutch defender has had a relatively successful loan spell in the championship this season. He has played a total of 42 games in all competitions and scored two goals for Coventry City.
#1 Ivan Perisic (Inter Milan)
Another player who could also be considered to replace Alonso, albeit an unconventional choice for the position, is Croatia international Ivan Perisic.
The 33-year-old could offer a whole lot to Tuchel's team in terms of experience, contribution and also versatility.
Perisic is arguably one of the most versatile players in Europe. He can operate in a handful of positions such as striker, wing-back, midfielder and winger, which could be an advantage for Chelsea.
He is yet to commit his future to Italian giants Inter Milan. This could provide an opportunity for the Blues to swoop in for his signature as a free agent, thus saving money in the transfer market. According to Italian outlet Corriere dello Sport (via Football Talk), Perisic is eyeing an offer from an English club and the Blues are one of the possible names.
Perisic has been outstanding for Inter Milan this season, making 48 appearances, scoring nine goals and providing nine assists in the process.
Where does Mane rank in Paul Merson's 5 greatest Liverpool signings of the Klopp era? Click here