The 27-year-old was Feyenoord's skipper last season and is one of the candidates to wear the armband while club captain Stiliyan Petrov continues his fight to beat leukaemia.
Vlaar, signed for just £3.5million, said: "Maybe I will be captain, you never know - but I just want to play and be important for the team.
"It was nice to be captain of Feyenoord. It made me a better player because it's not only about what happens on the pitch, but off it.
"I learned a lot about leadership, which is something I want to continue here.
"I have to get used to the way things are said in games. I look forward to that. I want to be a leader."