The Spain international is poised to move to Old Trafford in search of more regular game time, with his first-team opportunities at Camp Nou having been restricted last season by the sensational form of the Blaugrana's front three of Lionel Messi, Luis Suarez and Neymar.
Pedro is expected to link up with Van Gaal in Manchester after the Supercopa de Espana, with Neymar's contraction of the mumps leading to Barcelona asking the 28-year-old to delay his £22.3 million transfer in order to provide cover the double header with Athletic Bilbao.
However, Bulgarian icon Stoichkov, a five-time La Liga winner and European Cup champion with Barca who fell out out with Van Gaal in 1998, says that Pedro need only look at the way in which former Blaugrana goalkeeper Victor Valdes has been ostracised at Old Trafford to understand how perilous playing under the Dutchman can be.
"I would never be under the orders of Van Gaal," the 49-year-old told Spanish radio Onda Cero. "He's mediocre.
"He destroyed Barca and is destroying Manchester United.
"With what he has done to [Victor] Valdes he has shown he is a bad person. Hopefully Pedro listens to me and doesn't leave."
This is not the first time Stoichkov has taken aim at Van Gaal as he blames the ex-Barca boss for his Camp Nou exit 17 years ago, branding his former boss as "scum" in an interview with French newspaper L'Equipe in March.
"I have no respect for him," Stoichkov added.
"One day, when I was injured, I was with my wife at Camp Nou and Van Gaal went up to her.
"He asked her how it was possible that she married someone like me. She responded that I was a Ballon d'Or winner.
"My departure in 1998 was the fault of Van Gaal, for sure."
