The centre back, also known as Marlon Santos, joined the Catalan club in 2017 after a successful loan spell from Fluminense, where he made two senior appearances and featured heavily for the Barcelona B side.
Following his permanent arrival at Barcelona, Marlon has spent the this season in France with Nice, where the Foxes have kept a close eye on the potential transfer target to replace the outgoing Robert Huth.
During his two years in Ligue 1, the Brazilian has made 20 league appearances - including making his debut for Les Aiglons in a 4-0 win over AS Monaco.
Nice are understood to have an option to buy as part of that loan deal - though Leicester could look to hijack negotiations midway through by offering the same money as the French side, and higher wages to tempt the player.
The allure of Premier League football might be enough to tempt the talented Brazilian, but Leicester would be required to spend significantly to secure his work permit.
The central defender is uncapped at senior level, despite impressing in the Brazilian Under-20s setup.
This means the Foxes would only be allowed to bring him in if the fee and salary are at the levels recommended in the permit guidelines.
Should a deal for Marlon go through, it won't be Leicester's first piece of business in this summer however window, with the east Midlands club having already announced a deal for Porto star Ricardo Pereira.
Portuguese international Pereira joins the Foxes in a £22.5m deal, having agreed a five-year contract with the Premier League club.
The 24-year-old right back is highly rated, with some tipping him to become one of Europe’s best in his position.
He links up with compatriot Adrien Silva in Claude Puel's side as the Frenchman looks to strengthen the former Premier League champions.