The Dutchman, who won the Player of the Year award last season, swapped the Emirates for Old Trafford last summer in a controversial £24milion deal.
The 29-year-old enjoyed an explosive start at United, scoring 23 goals in his first 31 appearances to help his new side blow away the rest of the field.
However, Van Persie is without a goal for this club since the Premier League win over Everton on February 10.
And speaking to Inside United magazine, manager Ferguson suggested the drought be because his star man is in uncharted territory.
The Scot said: ‘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.’
Ferguson’s timing was curious, considering United’s season is effectively over with their Premier League lead seemingly unassailable and them now out of all three cup competitions following defeat to Chelsea in the FA Cup on Monday.
Arsenal, meanwhile, are, as they have been the previous two seasons, locked in a battle for a top four place with rivals Chelsea and Tottenham, giving each of their remaining eight Premier League matches meaning.
Wayne Rooney should return to the Manchester United squad for their crunch derby against rivals Manchester City after missing today’s FA Cup replay at Chelsea.
Ferguson claimed Rooney, who also missed his side’s 1-0 win at Sunderland on Saturday, picked up a groin injury on intentional duty.
Rooney played the full 90 minutes in England’s 1-1 draw with Montenegro on Tuesday, and was expected to feature in today’s last-eight replay at Stamford Bridge.
But Ferguson didn’t take a risk on the England international instead opting for Javier Hernandez with Robin van Persie on the bench.
“He got a groin injury playing for England and he wasn’t 100 per cent yesterday,’ Ferguson told ITV before today’s lunch-time kick-off. “There’s no point risking a player with a groin injury. ‘Hopefully he’ll be ready for next Monday’s game.” — Mailonline.



