Former Southampton boss Nigel Adkins says Manchester United fullback Luke Shaw struggled with his fitness early in his career.
Adkins gave Shaw his first team debut while in charge of Saints.
"We actually put a little group around Luke to support him, because physically he couldn't play 90 minutes of football," he told talkSPORT. "He barely even played 90 minutes for the Under-18s.
"I played him in the Premier League, but how could you only play him for half an hour?
"He was only 16 or 17, and he physically couldn't do it.
"We needed to allow him to grow into his body, but he had this unbelievable burst of acceleration. And you could see he was a talented player.
"I think if you're going to be a top player you'd probably have made your first team debut by the time you're 17, but it's all about how, as a manager and as a club, you nurture them through that period of time."