Manchester United legend Andy Cole is concerned about the development of Mason Greenwood - if United complete the signing of Jadon Sancho.
It appears the English winger is United's no.1 target this summer, even though Borussia Dortmund are playing hard ball over a fee.
Cole would not mind seeing Sancho at United, but he hopes it does not disrupt the rhythm and progression of Greenwood.
"Mason is scary, absolutely scary," Cole told the PA news agency. "If this kid lives up to his potential, United have one on their hands.
"It's scary and long may it continue. He needs to keep doing what he's doing, scoring goals and putting pressure on those up front, and as he matures and learns the game even more United have a player who could be anything.
"He can play as a nine and he can play out wide of a three, so it will be interesting to see where United think his best position is and what they see him as.
"For me, the best number nine in the world is Robert Lewandowski. But there aren't many, if any, Lewandowskis about. And if they do bring in Sancho then you've got to be careful as you don't want to block his (Greenwood's) progress.
"United do need to bring in players as you must improve every season but it's a fine balance. If you have a player like Mason Greenwood then you can't afford to block their progress."
