Ferguson admits bid for Van Persie
"We have made a bid," Ferguson told his club's website. "We're trying our best but there's no progress at this moment in time.
"We're not getting any breakthrough with Arsenal. I don't know what their thoughts are because they're not giving anything away."
Van Persie announced in July that he would not be extending his contract with the Londoners because he was unhappy with the direction they were taking.
The 29-year-old, who has one year remaining on his contract, has been with Arsenal since 2004.
Van Persie was the league's top scorer last season with 30 goals, three more than United spearhead Wayne Rooney who finished in second place.
The new season kicks off on August 18.