Ben White was worried about his ability to live up to Marcelo Bielsa's demands at Leeds United in his first week training under the Argentine this season.
The Yorkshire giants swooped to snap up White on a season-long loan deal from Premier League side Brighton & Hove Albion in the summer.
White is flourishing at Elland Road and has been watched by Liverpool and Manchester United, amid speculation he could soon be the subject of a big money bid.
However, the 22-year-old was left unsure whether he could physically handle the demands Bielsa places on his players in his first week of training at Leeds, according to The Athletic.
He confided in those close to him that he was concerned about whether his body could cope with the intensity demanded by Bielsa.
White got through the tough regime implemented by Bielsa and is now a key man at Elland Road.
The centre-back has made Leeds fans forget about the departure of Pontus Jansson, who was sold to Brentford in the summer transfer window.
Leeds have the best defensive record in the Championship this season, conceding just nine goals in 16 league encounters.
