"Without a shadow of a doubt he's the best player in the world at the moment," Brown told Manchester United's official website.
"He's taken his game to a different level and I'm sure he'll get more goals this season. I'm just glad he's on our side.
"Even for his team-mates, it's exciting to watch him when he gets on the ball because you know there's a chance something's going to happen, whether it's him setting up a goal or scoring one. He's capable of producing something out of nothing."