Jesse Lingard in action for United
The 23-year-old attacking midfielder is playing under his fourth manager at Old Trafford, having made his debut towards the tail-end of Sir Alex Ferguson's tenure before playing under David Moyes and Louis Van Gaal.
The Warrington-born Lingard has spoken of how much Mourinho's demeanour has surprised him.
'He takes all the sessions,' said Lingard, as quoted by the Mirror. 'While he wants us to work hard, he is always cracking jokes and having banter with the players.
'I thought he'd be very strict but, even though he works us hard and his mind is always on the job at all times, he also has a joke with the players.'
Lingard also remarked that the self-styled "Chosen One" has an 'aura' about him.
Mourinho knows what needs to be done to win trophies
Mourinho's light-hearted approach to training is all the more novel for United's squad given the management style of his predecessors.
The Telegraph reported that Van Gaal's method was 'academic' and 'sometimes overbearing'. His press conference references to his pursuit of "philosophy" merely added to the feeling that LVG was too statistical and headmasterly for a club with United's history and ethos of exciting football.
Before that, David Moyes had struggled to translate his successful template at Goodison Park to Old Trafford.
Manchester Evening News reported that during the Moyes era there were multiple rifts within the club as players grew disillusioned with the Scotsman's methods.
David Moyes, sacked from Old Trafford after 10 months, has just taken over at Sunderland
The poisoned chalice that manager of Manchester United has become since Ferguson retired shows that player happiness is vital to success at the club.
While squad contentment can be guaranteed by success on the field - and in Mourinho United now have a manager who has achieved great success everywhere he has been - having a laugh and a joke with his players will certainly go a long way to bringing back trophies to United's overflowing cabinet.
Lingard will hope to continue his new-found habit for shooting United to cup final glory. Having scored the winner in extra time of last season's FA Cup final against Crystal Palace, he opened the scoring in last weekend's Community Shield victory over Leicester City with a sensational solo goal.
Lingard gave United the lead last weekend with a brilliant 40-yard run