Liam Cooper has thanked Marcelo Bielsa for helping him transform his Leeds career.
Leeds have just handed Cooper a new five-year contract in a huge sign of their faith in Bielsa's skipper.
He has developed enormously since Bielsa arrived at Elland Road 15 months ago and was named in last season's Championship Team of the Year.
Cooper's success now is in stark contrast to the troubles he endured when he signed from Chesterfield for £600,000 in August 2014 when he admits even he questioned himself.
He struggled to establish himself at Elland Road as the club rapidly went through a succession of managers.
His red card in Leeds' embarrassing FA Cup defeat at Sutton United in January 2017 appeared to spell the end of his time at the club before Thomas Christiansen arrived that summer to give him a fresh start.
Cooper, 28, grabbed it and has blossomed under Bielsa to become an accomplished, ball-playing centre-half and the team's leader.
Steve Clarke rewarded the Yorkshire-born centre-half's progress by handing him his first two Scotland caps this month and the former Hull trainee is delighted by the turnaround in his fortunes.
"The first three-and-a-half years I really struggled under different managerial staff and it was hard," he told LeedsLive.
"You do start to question yourself and whether you are good enough and whether you can do it at this level
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"It's hard at times. We're there to be shot at as players and as individuals and it doesn't just affect us, it affects families.
"I've come out the other side. Marcelo coming to the club has been a massive plus for me. I see the game from a whole different perspective now.
"The way you should apply yourself and the way you go into games. It's all or nothing and that's the way it's got to be." Leeds also handed Northern Ireland international Stuart Dallas a new four-year deal 48 hours after tying Kalvin Phillips down with a five-year deal as they plan for the future.