Over the weeks in the summer transfer window, Van Persie has been linked to several clubs like Juventus, Manchester City and United. Some reports claim that the Dutch star will remain at the Emirates after joining the teams camp in Germany.
However, the 28-year-old is willing to join United only if his salary matches Wayne Rooney's £220,000-a-week. Italian champions Juve have had a £190,000-a-week offer rejected while Manchester City are no longer in the race to sign the Gunner.
Meanwhile, United are in pole position to seal the deal but Ferguson feels Arsenal are reluctant to finalise any offer.
"We have made a bid and they've been trying to negotiate with other clubs, Ferguson said after his side's pre-season friendly loss to Barcelona.
"I don't have a gut feeling on it at the moment, I must admit. We're not getting any breakthrough with Arsenal. It's difficult to say why they're operating this way. I don't know what their thoughts are because they're not giving anything away," he said.
Earlier in July, Juventus, City and United had bids rejected by Arsenal after they failed to meet the Gunners valuation of £20m. Now, Arsenal are demanding £5m more from United if they want to sign Van Persie.
"I can't give you any more information. We just have to persevere. We are trying our best and hopefully it will come our way but there's no progress at this moment in time," Fergie said.
United's top target Lucas Moura has signed a four-year contract with France Ligue 1 side Paris Saint-Germain. PSG, owned by Qatari billionaires, splashed £32m for the 19-year-old Brazilian playmaker and is expected to join the cash-rich club in January.