Veltman played under ten Hag - who will take over at Manchester United this summer - for two and a half years at the Dutch club.
"Yeah [he made us better players], especially against big opponents," the Dutchman told MUTV.
"I think we showed that in the Champions League run that we had, three years ago.
"He knew where the weaknesses were in the big opponents. Sometimes, you don't need to be the better team but if you are a team, you can have great results."
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