Manchester United midfielder Antonio Valencia admits he is surprised by the massive improvement of teammate Rafael.
The Brazilian right-back has been a key contributor for United this season as they pursue a 20th league title with a 15-point lead over the rest of the Premier League clubs and Valencia believes he can become one of the best players in the world in his position.
"It's incredible how much he's improved," said Valencia. "I've seen a big improvement in his level of concentration.
"If he continues, it won't be long before he's one of the best right-backs in the world."
