Even though the Red Devils claimed a record 20th championship by an imposing 11 points last term, Chelsea and Manchester City are tipped to overhaul them.
The reason is obvious. The man who guided United to an incredible 13 Premier League titles is no longer at the helm.
So, whilst Manuel Pellegrini has to get used to life at Manchester City and Jose Mourinho has returned to Chelsea, but with a group of players that do not seem to fit with his philosophy, the argument goes that United are in peril.
The theory does not really make sense, certainly not to van Persie.
"They can think what they want to think," the Dutchman told the Guardian.
"It doesn't matter to us. What matters to us is the way that we work.
"Trust me, we will work very hard. It's a huge challenge to all of us and it is one we are looking forward to."
Van Persie took a risk by leaving Arsenal at this time last year.
But it paid off handsomely as the Dutchman's prolific form during the first two-thirds of the campaign allowed United to open up a massive gap on their rivals they eventually had no hope of closing.
Van Persie also collected another Golden Boot prize to add to the one he claimed during his final season with the Gunners.
And it is clear, there is much more for him to do.
"I just see big opportunities. I still have more years left and it's not like I am saying: 'Yeah, we won the league so that's me done'," he said.
"I want more now. It makes me even more hungry.
"We have a great bunch of players so we can win do better."