That potential deal means that Van Gaal still needs to bring in another player to inject some pace in to his front line - and now he appears to have turned his attention to Mane.
The Telegraph suggest that United have contacted Southampton over a deal for Senegal international Mane, who enjoyed a superb debut season in the Premier League last term.
The 23-year-old hit ten goals in his first season at Southampton having joined from Red Bull Salzburg last summer, establishing himself as one of the most dangerous wingers in the Premier League due to his blistering pace and superb trickery.
Now, it seems that his performances on the South Coast have triggered interest from United, who recently snapped up his former team-mate Morgan Schneiderlin.
Southampton will no doubt fight tooth and nail to keep Mane at St. Mary's Stadium given his importance to Ronald Koeman's system, but the lure of Old Trafford may turn Mane's head - just as it did with Luke Shaw over a year ago.
Fans may not get quite as excited about Mane as they were about Pedro, but United would be landing a proven Premier League threat - and the combination of Mane and Memphis Depay out wide could turn United's pedestrian attack into one to be feared.