The 29-year-old striker has been in poor form in recent weeks, and after his strike against Sunderland was deemed to have been a Titus Bramble own goal instead, his goalless run now stretches to 10 league games.
Nevertheless, with the Premier League title seemingly in the bag, with a 12-point gap established over rivals City at the top of the table with just seven games left, Stam feels Van Persie has already proven his quality and that there is more to come from him this season.
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"Although I've heard people talking about him not scoring for a while, I think he's scored a lot before that and, when he gets chances again, he will score goals for United in the future.
"He's done exceptionally well and is a world-class player who has proved himself in England really well since he left Holland. So everyone has got a lot of respect for him for what he's done in his career."Robin has been very important for the club. It's hard for strikers to score in every game and to finish off every chance that they get.
"It's not like that in football. The opponents always know the quality of the strikers so, if van Persie is scoring, a lot of other teams will be marking him with two defenders and making it hard for him to score.
"But it doesn't matter as he's then taking a lot of attention away from the defenders and, if someone else scores, as they have been doing, then it's okay."