Koeman has offered his opinion of how his old boss manages players differently to himself.
Koeman's fractious relationship with the Manchester United manager is well documented and his latest comments will probably do nothing to heal it.
He is quoted in the Daily Mirror, saying: “When you bring Van Gaal in the house, you bring in quality. But you also bring in someone who thinks he knows everything. And that will cause clashes.
“There is a big difference between him and and me as managers. I was his assistant at Barcelona after the World Cup in 1998. I learned a lot of things from him.
“But the way he handles his players is totally different from the way I work. I don’t put as much pressure on the shoulder of players.
“When you have Van Gaal in charge, it is a fact that there is fear in his team. The players have a fear for mister Van Gaal. That is not always good.”
Given the respective environments the pair operate in, it's arguable that their current managerial positions are suited to their style of management.
Louis van Gaal is in the more high pressure, more highly scrutinised environment of Manchester United, a well-known footballing brand that attracts support from all around the globe. Though he may have taken over a side that failed to live up to the heights of that managed by Sir Alex Ferguson in David Moyes, there is still this massive expectation to be successful at Old Trafford.
Koeman arrived under very different conditions as he was given the task of rebuilding the side but his approach appears to have helped deliver some rapid progress which has him competing with van Gaal's side despite the club being vastly inferior in stature and expectations at the start of the campaign.
Though some will point to improvement that van Gaal has brought to Old Trafford, the job Koeman has done at St Mary's is nothing short of stunning given the amount of changes that happened at the club. His approach at getting the best out of the players at his disposal seems to have worked so far this season.