The Colombian, who has been on United’s bench for their last five matches, has scored just four goals during a season-long loan deal from Monaco.
Van Gaal has the chance to add Falcao to his squad on a permanent basis for £43m in the summer but Argentina World Cup winner Maradona insists he has not been given a chance to show his worth at Old Trafford.
Speaking at a press conference to promote a charity match in Bogota, Colombia, Maradona said: “Van Gaal is not a nice guy. Van Gaal is closer to the devil than anything.”
Maradona, who watched United lose at home to Liverpool last season, is convinced the serious knee injury which Falcao picked up last year has hindered his ability to adapt to conditions in England.
Falcao, 29, was forced to miss the World Cup last year because of the injury and has also been troubled by a series of niggling problems since the start of his loan deal last August.
“His time was cut short after the injury and he has to adapt to the move,” Maradona said at the press conference shown on the YouTube channel of TV station Canal Capital.