The former Arsenal ace says that the Dutchman is being unfairly treated.
The Dutchman's job at Old Trafford has come under intense scrutiny these past few months after United failed to reach the latter stages of the Champions League, coupled with a short-lived Premier League title challenge.
Injuries have not helped his cause in a campaign which has seen so many of his established players endure spells on the sidelines, forcing van Gaal to dig into the club's reserve of academy prospects in recent weeks.
Eighteen-year-old Marcus Rashford, who has netted four goals in his first two senior appearances, is among those to have felt the benefits of van Gaal's faith, and ex-Arsenal man Merson feels that the former Netherlands coach should be commended rather than criticised.
"I feel sorry for Van Gaal a bit," Merson told Sky Sports. "He could have come into United and spent all that money on 28-year-olds, proven footballers who have won things. That might not have helped the club in the long term but it may have delivered a trophy. However, in three years time it would leave the club in a worse place than they are now.
"But he hasn't done that. He went out and has bought youngsters for the future and has given other youngsters a chance. It's not the same as [Arsene] Wenger, who has been manager for almost 20 years. Van Gaal has been there for less than two, so it's a completely different case.
"He has bought players for the future for United as a club. He's not thinking of himself, he's hoping they are going to be in a better position when he leaves."
After seeing his first season somewhat tarnished by the failings of Angel di Maria and Radamel Falcao, undoubtedly at a world-class level at the time of their arrival, the Red Devils boss largely signed players on potential last summer, with Matteo Darmian, Anthony Martial and Memphis Depay among those coming in.