The centre back spent the duration of the season on loan with Nice as part of a two-year agreement after Ernesto Valerde saw Marlon as surplus to requirements for the season, despite only putting pen to paper on a permanent deal for Barcelona last summer.
The Brazilian was a regular starter for Nice this season, featuring in 27 games in all competitions, where his consistent performances caught the eye of several clubs from the Premier League, including Leicester City and West Ham.
However, according to Mundo Deportivo, the Hammers are in pole position to land the 22-year-old as the Spanish giants are now simply awaiting a formal offer to take negotiations to the next stage.
West Ham have already been in contact with both Barcelona and Nice as the latter possess an option to sign Marlon permanently at the conclusion of the loan deal which ends in 2019.
Marlon spent a year with Barcelona B following his move from Brazilian side Fluminense in 2015 before making both his La Liga and Champions League debut for the club under Luis Enrique last season, where he made a total of three appearances for the first team.
In other news, West Ham star Marko Arnautović has been mooted as a potential summer transfer target for Jose Mourinho as the Manchester United boss looks to bolster his attacking options ahead of next season.
Arnautović worked alongside Mourinho at Inter in season 2009/10, but is said to be 'one of several options' for the Red Devils.