Van Gaal spent two seasons in charge of the Red Devils between 2014 and 2016 but was sacked after winning the FA Cup in his final season and replaced by Jose Mourinho.
Man United will appoint a permanent manager at the end of the season as Rangnick is currently on an interim role and Van Gaal's compatriot Erik Ten Hag has been earmarked as a potential appointee.
But Van Gaal has warned the Ajax Amsterdam boss against making the switch to Old Trafford, describing his old side as a 'commercial club'.
Rangnick has leapt to the defense of Man United, insisting that their model of operation is no different to that of their rivals.
"Louis himself as an experienced coach signed a contract here some five or six years ago, and he could have known that in advance if he had that opinion," Rangnick said.
"I think football worldwide and even more so in the English Premier League – when any rich person or company can buy a club, as long as they pass the fit and proper person test – is a commercialised business, that's for sure. No matter which club in which city.
"What I can only tell you from the last four months is that this is a club with a big tradition with a close relationship with the supporters and to the whole city, region and area.
"For me, it's a great club, and if the club draws the right conclusions on what's happened in the last couple of years... Yes, the last couple of years have not been as good as expected, but if they draw the right conclusions, I still see a very bright future for this club."
