Hristo Stoichkov says his former Barcelona coach Louis van Gaal is "destroying" Manchester United, and warned Pedro Rodriguez not to move to Old Trafford.
Stoichkov won five La Liga titles and the 1992 Champions League as a Barca player but left the Camp Nou shortly after Van Gaal's arrival in 1997.
The Dutchman went on to win two La Liga titles and a Copa del Rey in his first spell as Barca coach, which ended in 2000, but his second stint, in the 2002-03 season, was much less successful and was marred by a row with Rivaldo.
Stoichkov, now a radio pundit in Spain, told radio show "Al Primer Toque" that Van Gaal could not get on with top players.
"[Van Gaal] makes the players suffer, as he was such a mediocre player himself," the former Bulgaria international said. "He is destroying all the players, as he is so mediocre -- look at the players who have left because of him. First he destroyed Barcelona in that era, then it takes many years to rebuild."
United have invested heavily over the last two summers, but Stoichkov said he was unimpressed with their performance in Saturday's Premier League opener against Tottenham, when a Kyle Walker own goal gave them a 1-0 win.
"Now [Van Gaal] is spending €200m, and the other day I saw their first game in the English league -- disastrous," he said. "They won 1-0 with an own goal and he is happy."
The forward did not arrive at Barca until after Van Gaal's departure, though, and Stoichkov said the Spain international would damage his career if he moved to Old Trafford.
"I would never let Pedro leave, never, because if he goes there he will stop being a player," he said. "I hope Pedro listens and says: 'I'm staying at Barcelona.'"
There have been conflicting reports as to whether the €30m release clause in Pedro's contract can be triggered this summer, but it has been suggested that Barca were willing to cash in to balance the books after spending over €50m on Arda Turan and Aleix Vidal this summer.
Stoichkov, though, said that La Masia graduate Pedro's commitment to the club was more important than any financial concerns.
"Barcelona does not need money -- it doesn't matter if it is €20m, €30m or €50m," he said. "Pedro is a symbol of barcelonismo, Pedro is a guy who never ... I would never sell a guy who is so committed, a guy with energy, who fights to be a great player."