Chelsea are closing in on signing left-back Alex Sandro from Juventus for £61 million -- an eye-watering fee that would make the Brazilian the most expensive defender in the history of football.
Sandro, 26, is often hailed as one of the most accomplished wing-backs in the world. But as recent history shows, a lofty billing or price tag is no guarantee of success in a position that has proven to be an expensive headache for Chelsea since the departure of Ashley Cole in 2014.
ESPN FC takes a look back at the players who have been tried in Chelsea's problem area on the left side of defence in recent years.
*Dates and figures relate to how long and how many times each player was used on the left side of defence
Filipe Luis (July 2014-July 2015, 26 appearances)
Signed from Atletico Madrid for £15.8m in the summer of 2014, Filipe Luis seemed the ideal replacement for Cole: positionally smart, tactically disciplined, mobile and comfortable on the ball. In Spain, he had been a key part of the most brutally efficient defence in Europe.
Yet it quickly became clear that the Brazilian was not a good fit for the English game. After looking sluggish and unsure of himself on the pitch, he failed to displace Cesar Azpilicueta as Jose Mourinho's first choice left-back. He started just nine Premier League matches before being sold back to Atletico.
"I did not adapt the way I wanted to, and I was never a sure starter," Filipe Luis told ESPN Brasil last month. "It was a good experience but I struggled. I had to play against fast and strong players... I had good games there. I was able to lift trophies, and played 26 games with Chelsea. But I am happier in Spain."
Cesar Azpilicueta (October 2013-September 2016, 102 appearances)
Signed as a right-back, Chelsea fans were first made aware of Azpilicueta's remarkable adaptability early in the 2013-14 season, when Mourinho began starting him regularly at left-back at the expense of an ageing Cole.
The Spain international proved so dependable that he was voted the club's Players' Player of the Year. Cole was allowed to leave on a free transfer the following summer, and the man widely expected to be his replacement (Filipe Luis) failed to establish himself in the starting XI.
Ryan Bertrand was another casualty of Azpilicueta's inexorable rise, eventually making his loan spell at Southampton permanent in February 2015 after becoming disillusioned by a lack of opportunities at Stamford Bridge.
Tireless, tenacious and relentlessly focused, Azpilicueta provided every quality that Mourinho looks for in his full-backs, although his need to cut inside onto his stronger right foot curtailed both his and Chelsea's attacking potential. Yet now he's almost unmovable as the left-sided centre-back in Antonio Conte's back-three.
Baba Rahman (August 2015-August 2016, 23 appearances)
A signing necessitated by Filipe Luis' return to Atletico, the start of Baba's career at Chelsea wasn't helped by arriving too late to be involved in Mourinho's preseason preparations. He began the 2015 campaign as back-up to Azpilicueta.
Although the Blues' season quickly descended into disarray, the Ghanaian started just 11 Premier League matches -- the majority of which came after Mourinho had been sacked, and interim successor Guus Hiddink began experimenting with the youngsters on the fringes of Chelsea's first-team squad.
Fast, technically accomplished and a dangerous crosser, Baba showed flashes of attacking promise from left-back, but exposed himself as a defensive liability. Hiddink even substituted him at the halfway mark of a Premier League clash with Southampton after he had gifted Shane Long the opening goal of the game.
Conte assessed Baba in preseason before sanctioning a loan move to Schalke, where the Ghanaian was used as a winger and also as a full-back before tearing the anterior cruciate ligament in his left knee in January.
Kenedy (June 2015-August 2016, eight appearances)
The most fleeting of all Chelsea's left-back experiments, Kenedy was given a chance to impress as part of a back-four and back-five by Hiddink.
A winger by trade but relatively tall and powerfully built, the Brazilian enjoyed some good moments -- most notably surging forward to score against Norwich City after just 39 seconds in March 2016 -- but never entirely convinced as a defender, and Hiddink moved away from the idea before the end of the season.
Kenedy seemed a nice fit for Conte's 3-4-3 system when recalled from an unsuccessful loan spell at Watford in January, but never earned the Italian's trust. Overall, he played just 16 minutes of Premier League football last season, and is likely to be sold or loaned out this summer.
Marcos Alonso (August 2016-present, 35 appearances)
A signing greeted with derision by many Chelsea supporters who remembered his unremarkable days at Bolton Wanderers and Sunderland, Alonso has proven himself to be an inspired piece of business, and played a key role in returning the Blues to the pinnacle of English football.
The 26-year-old's stamina, technical ability and intelligent crossing -- not to mention a habit of scoring important goals -- made it possible for Conte to switch to the 3-4-3 system that won Chelsea the Premier League title, even if his athletic limitations and weaknesses as a one-on-one defender can be problematic.
There is no doubt that Alonso will continue to be an important player for Chelsea, but it's also easy to understand why Conte has identified the Spaniard as an easy starter to upgrade -- particularly with a player as gifted as Sandro waiting in the wings.