The Red Devils have struggled for goals this season, and Merson believes that it could be down to this move.
The Portuguese winger spent last season out on loan with Sporting Lisbon, before joining Fenerbahce in a permanent deal this summer, and with United struggling for goals, Merson believes that Nani could have been the answer to their problems.
"I think he's been a big miss. I know he can be hot or cold but when he did it, he really did," he said.
"Lingard scored a great goal to get his manager out of trouble against West Brom but again you're talking about a young lad against a player who has played for Portugal a million times
"If you're a full-back then you'd definitely rather face Lingard or Adnan Januzaj," he explained.
United's struggles in front of goal have often been put down to their lack of striker options, as well as the poor form of Wayne Rooney, but Merson clearly feels that the problem stems from their lack of genuine wingers in the squad.
As well as Jesse Lingard, van Gaal has few senior options. Memphis Depay has shown glimpses of real quality this season, but they have not been frequent enough to carry the burden.
Ashley Young is the only winger with a large amount of Premier League experience, and yet he has been restricted to mostly substitute appearances and has often been deployed in a deeper role.
Meanwhile, Nani has shone during his first few months in Turkey. He has six goals and four assists, which, in both categories, is a greater number than any United player has achieved in the top flight this campaign.