Brown told BoyleSports, who offer the latest Club World Cup odds: "Marcus Rashford is going to have to start playing really well wherever he goes, first of all. He's done well at Aston Villa, he's got his head back in the game. But he still has two years on his contract at United.
"If he is looking to move, he would obviously want a big club and Barcelona would be ideal. But it's a lot of money. If the club is looking to get rid of him, they're probably wanting to get paid as well.
"It's not an easy one to sort out, talking from my heart, I think it would be brilliant if Ruben Amorim and Marcus could sort things out.
"When he's on form, it's a player United have really missed. I hope they can sort it out in a way that everybody gets what they want. For Marcus personally, he just needs to get his head down and play some football now.
"Hopefully this gets sorted out sooner rather than later."