The former Villa man worked with Koeman at Feyenoord.
Southampton boss Ronald Koeman has received plenty of praise in recent times for his work at St Mary's. He received a depleted squad after Mauricio Pochettino left for Tottenham Hotspur but worked wonders with it, creating a team now established in the Premier League.
He told Voetbal International this week that he finally began to get his career going after a year working with Koeman in 2011.
"My first full season after the injury period ended in 2010. I just missed out on the World Cup squad. I could live with that.
"Then came the dramatic year in which we were tenth with Feyenoord and I was out of the picture at the Dutch national team.
"I'm only thinking differently after the arrival of Ronald Koeman in 2011. Feyenoord was back on the rise and for me personally that had consequences. I set myself more requirements and new goals."
Vlaar, who is currently training with AZ Alkmaar in a bid to recover from meniscus surgery, is not the only man to praise Koeman in recent times.
The Southampton boss has received plenty of praise in his time in English football and rightly so considering the way he has carried on the good work of Pochettino.
The Dutch international, who left Aston Villa on a free transfer this summer, is simply echoing the thoughts of many who continue to be impressed by Koeman's work on the south-coast.