The Brazil international has been heavily linked with a move to the Premier League side for much of the past 18 months, despite having signed a new five-year contract last October.
The forward's agent, Wagner Ribeiro, claimed last September that he had been tempted by offers from United and Paris Saint-Germain, who were reportedly ready to pay a transfer fee of up to €190million.
Speculation of renewed interest from United has refused to die down, even though manager Jose Mourinho stated in May that it would be "absurd" to try to sign the player.
Neymar has admitted that he cannot guarantee his long-term future but offered something of a tongue-in-cheek response when asked where he could potentially move.
"Who knows what will happen tomorrow?" he said after the Neymar Jr's Five event. "I'm very happy for now, very well adjusted. But anything can happen, who knows."
Asked if he could go to United, he replied: "Yes... or Eibar!"
The 25-year-old had earlier stated that he believes 2017-18 will be the most important campaign of his career.
"I hope it will be a season with a lot of success and a lot of happiness," he said.
"I'm getting ready for it. It's going to be one of the most important seasons of my life. It will be the most important season of my life.
"So I'm really happy and really excited, and I'm going to start training and get prepared."