Manchester City just keep getting better.

Fresh off winning a historic treble last season, Pep Guardiola's team is set to bolster its already stout backline with the addition of Croatian star Josko Gvardiol. After lengthy negotiations, the English club finally reached an agreement with RB Leipzig over a fee for the standout defender, according to transfer insider Fabrizio Romano.

Leipzig director Max Eberl said earlier this month that the two clubs were locked in talks about a deal worth "€100 million plus bonuses."

That figure, which equates to roughly £86 million, would make Gvardiol the most expensive defender in history, eclipsing the £80 million that Manchester United spent in 2019 to acquire Harry Maguire from Leicester City.

The record-breaking transfer is imminent after Gvardiol, 21, completed the first part of his medical test on Wednesday, Romano adds. Personal terms have long been agreed between the player and Premier League champions.

City have been mentioned as a potential destination for Gvardiol dating back to last season. Chelsea came close to landing the left-footed center-back with a reported €90-million offer last summer but couldn't get the deal over the finish line before turning their attention to other targets.

Gvardiol, a product of the Dinamo Zagreb youth system, joined Leipzig in 2020. His reputation skyrocketed in the Bundesliga, while a superlative performance anchoring the Croatian backline at the 2022 World Cup in Qatar made him one of the most sought-after defenders in the world.

He showcased some of his talents against his soon-to-be employer in February, scoring a towering header to equalize versus City in the first leg of their Champions League last-16 clash.

City thrived last season after Guardiola decided to eschew natural full-backs in favor of different systems that used three - and sometimes four - center-backs on the pitch at the same time. Gvardiol, smooth in possession and quick enough to cover large areas of the pitch on his own, should, in theory, fit right in on the left side of Guardiola's defense.

His arrival could coincide with the departure of fellow lefty Aymeric Laporte, who has been linked with a return to Spain this summer.