In February, ahead of the Netherlands' 1-1 friendly draw against Italy, Van Gaal revealed that he perceived both domestic leagues to be on a similar level.
However, speaking to Sportschrijvert, Van Hanegem instead asserted that Dutch football was struggling to keep up in Europe, and barely attempted to conceal his distaste for the Oranje boss.
“Van Gaal is deranged,” he began. “How can you make that claim? It is good that he will leave again after the World Cup.
“I see our teams play and it’s a festival of colossal mistakes, which has nothing to do with good football. Do you see that in the Champions League?”
The 69-year-old was unrelenting in his denouncement of the Eredivisie, and slammed its participants, particularly his former club Feyenoord, for their lack of ambition both domestically and in Europe.
“We're struggling to even have three teams in Europe,” he continued. “They're only looking to cover their own backside. Make top five, upper half of the table, qualify for European football. Comments like that.
“After Feyenoord’s second and third finishes in recent seasons, the squad remained the same, so why not say that you want to challenge for the title?
“If you play for Feyenoord, Ajax and PSV, you need to get involved for the national title. Fortunately, [Feyenoord coach] Ronald Koeman now realises that as well, but he has yet to convince the players."
Van Hanegem spent 10 years at Feyenoord over two different spells during his playing career, and amassed 52 caps for Netherlands, scoring six times.