Both Vlaar and PSV Eindhoven star Depay are current members of the Holland squad.
Vlaar said, "Memphis will need to get faster and better. The threat he had in the Eredivisie, he might not have directly in the Premier League. And if he makes the same play several times, the defenders will adjust to his game.
"But Memphis has enough quality to increase his operational speed.
"He's shown he can quickly adjust to a higher level, namely at the World Cup."