Van Gaal had two spells in the dugout at the Camp Nou with the first stint seeing fellow Dutchman Koeman as his assistant before his disastrous return in the 2002-03 season.
Currently boss of the Netherlands, van Gaal won four trophies during his first tenure in the Barca hotseat including two La Liga titles.
But things eventually turned sour and he marked his departure with the iconic phrase: “Friends of the press. I am leaving. Congratulations.”
He has now launched an attack on the Catalan giants by alleging that the pressure Koeman is coming under at the club is fuelled by the fact he is Dutch.
When asked about Koeman’s position, van Gaal told a press conference that “history is repeating itself” in reference to the criticism he endured when results began to against him at the club.
He also advised his former assistant “not to pay much attention” to the criticism.
“It is typical Barcelona,” said van Gaal.
“When everything is going well and you make great contributions, as Frenkie de Jong has done in the last two years, then you do not have anything to worry about.
“But when things go wrong, the people at Barcelona will always look (to blame) foreigners.
“In this case, it applies to the coach, because he (Koeman) is a foreigner and Dutch.”
The comments come as Koeman comes under increasing pressure in the Camp Nou hotseat with his side struggling to gain results either domestically or in Europe.
Barca slumped to a two-goal loss at champions Atletico Madrid before the international break to follow on from underwhelming recent draws against Granada and Cadiz.
The Catalan club’s struggles in European competition are even more worrying with three-goal defeats in each of their opening two Champions League matches – at home to Bayern Munich, whom they did not register a shot on target against, and at Benfica.
That has led to club president Joan Laporta forbidding Koeman to give any media interviews, causing the Barca boss to cancel a pre-agreed conversation with Dutch TV this weekend.
Van Gaal is not the only former Barca employee who has spoken about his exasperation with the current situation at the club.
Former striker Samuel Eto’o has claimed that the side’s current results are making him ‘suffer’ and admits that these are ‘hard times’ for the giants.
The Cameroonian told Festival dello Sport di Trento: “Lately, Barcelona has been making me suffer. These are hard times for those of us who love them.
“It would be difficult to accept elimination from the Champions League group. I hope that does not happen!”
Former Barca defender Laurent Blanc has also spoken out against the club’s “monumental’ mistakes” in recent seasons.
Speaking of Lionel Messi leaving for PSG, Blanc told Panenka magazine : “If I look at it from the Barça side, I think they have made monumental mistakes. Monumental.
“Not only because of Messi, but for the last four or five years.
“They have lost incredible players a club like Barca should not be doing that, it is damaging.
“You can’t lose Neymar or Messi, because it’s very difficult to replace them.”