The Belgium defender is expected to sign for United after the World Cup.
"Thomas Vermaelen wants to play football," Parlour told talkSPORT. "Last year he couldn't get in the Arsenal side because Per Mertesacker and Laurent Koscielny were superb at the back. Kieran Gibbs has improved so much he couldn't even play him at left-back.
"When you get to a situation where a squad member wants to move, sometimes the player has more sway than the club itself.
"If he wants to play football, and an offer comes in from a club like Manchester United, then it's hard for the club to say, 'no, you can't go there, we want to sell you to a club in Italy or Spain'.
"He was doing the captain's notes last year in the Arsenal programme but not getting in the team. I can't see that changing anytime soon. He wants to play first team football."
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