Manchester United must be careful not to hinder Mason Greenwood's development if they sign a forward, according to former striker Andy Cole.
Greenwood was a revelation last season after boss Ole Gunnar Solskjaer put his faith in the teenager by selling Romelu Lukaku and loaning Alexis Sanchez to Inter Milan last summer.
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The 18-year-old scored 17 goals in all competitions for the first team, becoming a pivotal part of United's attack alongside Anthony Martial and fellow academy product Marcus Rashford.
United are keen to sign a right-sided forward - the position Greenwood primarily takes up in the team - with Borussia Dortmund winger Jadon Sancho their No 1 target this summer.
Cole, a treble winner with United in 1999, who scored 121 goals in 275 appearances for the club, is worried a big summer signing could block Greenwood's progress.
"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."