United endured a stuttering start to life under Van Gaal, failing to win four of the Dutchman's first five games in charge.
However, a run of just two defeats in 19 Premier League games has catapulted the 20-time champions firmly into the top-four race – they sit fourth, two points ahead of fifth-placed Liverpool ahead of their trip to Anfield.
And Rodgers believes Van Gaal has what it takes to enter the pantheon of United greats.
"Even he would say that coming into the Premier League is different to where he's worked before," the Liverpool boss said of his Old Trafford counterpart. "The competition in this country is far greater.
"He's shown over his career that he's a top-class manager. He'll have seen coming into this country for the first time, the challenges of football here.
"This is the most competitive league in the world. If you've spent your career in the Premier League, it's different to the other leagues.
"But I don't think you can argue about his credentials. He's put philosophies in place at Ajax, Barcelona and AZ. If he ever leaves United, he'll still have been one of the great managers.
"Manchester United will look to continue to stay in that top four. For us, the challenge is to get above them and into that top four."
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