The Dutch striker hit the ground running at Old Trafford, plundering 22 goals from 28 appearances after joining from Arsenal in the summer. However, he has now produced just one goal in his last 12 games.
The Red Devils take on rivals Manchester City on Monday evening and the Scot has hinted that Van Persie could be rested for the encounter.
"I've no worries about Wayne Rooney, because he's needing games," Ferguson told Inside United magazine. "He's the kind of player who has to play all the time.
"With Van Persie, we have to monitor it because we still don't know all about Robin, and the kind of seasons he's had. I don't think he had a season of such intensity during his time at Arsenal, so we'll have to look at that."
Van Persie's last goal came in the 2-0 win over Everton in February.