A stopwatch and a whistle round his neck, van Gaal wore an unrelenting critical glare as his players sprinted and slalomed through cones, lifted weights and medicine balls, and took part in resistance training with an elasticated band around their waists.
The scrutiny was intense. Nobody was allowed to slacken off for a second. If they did, he would issue a stern rebuke or send assistant Albert Stuivenburg to do it for him.
Push up: Van Gaal makes a point as the players perform one-handed press-ups using basketballs
When the players were granted a pause in the sticky Florida evening they looked knackered.
Test of strength: Striker Javier Hernandez gets to grips with the weights during the training session. The Mexican scored United’s third goal in their 3-1 win over Real Madrid on Saturday
It has become clear on United’s American tour that van Gaal is not only trying to instil a new tactical awareness in his players but also make them the fittest and strongest in the Premier League.
He had no problem with publicly embarrassing new signing Luke Shaw by saying he wasn’t fit enough and made him train on his own to catch up. It doesn’t matter if you’re the new £30m signing.
Strongman: Wayne Rooney takes his turn to lift the weights as pre-season training continues apace
Barking the orders: Van Gaal watches on as his assistant Albert Stuivenberg issues instructions
Hard work, lads? The players certainly looked as if they’d been put through a hard session
Van Gaal certainly looked every inch the PE teacher he had trained to become as he put his Manchester United squad through their paces ahead of Monday night’s International Champions Cup final with Liverpool.
The Sun Life Stadium in Miami resembled a ‘Boot Camp’ as the players were put through a gruelling session of circuit training.
Good start: United have won all four matches under van Gaal’s stewardship so far, against the LA Galaxy, Roma, Inter Milan and Real Madrid
Stung: New signing Luke Shaw was publicly criticised by van Gaal for not being fit enough
Tied up: The United players had elastic bands attached to their waists for some resistance training
Best foot forward: Goalkeeper Sam Johnstone at the end of a rope held by Shinji Kagawa
Hold on: Keepers Sam Johnstone (left), Anders Lindegaard (middle) and David de Gea take part in the resistance training part of the circuit
Roll with it: The players also used medicine balls and barbells during the circuit
Weighed down: Javier Hernandez smiles as he carries a weight
Slalom: Sam Johnstone steps through the cones as Kagawa waits for his turn behind
Jog on: Wayne Rooney and Tom Cleverley take part in the warm-up
Return: Darren Fletcher is enjoying his first pre-season in two years following struggles with illness
Get moving: The players size up the circuit as training gets underway in Miami
Even striker Robin van Persie, the ‘teacher’s pet’, has been told to prove his fitness before being allowed anywhere near the team.
Instructions are short and sharp, delivered in an authoritative tone. He’s not looking for a discussion, this is what’s going to happen.
His biographer Maarten Meijer captures this ‘schoolmasterly’ approach well in his recent book on van Gaal’s life.
‘The experience of daily interacting with often unmotivated or emotionally troubled youths at school has given these trainers a cutting edge,’ he writes.
In form: Ashley Young has scored four times on the American tour as he bids for a first team spot
Thoughtful: Assistant manager Ryan Giggs watches on as the squad train
‘This skills can be recognised in the way they deal with their adult charges – pro players – who can be just as testy and demanding as high school boys, and who intermittently require patient understanding and tough discipline.
‘Van Gaal’s critics are perturbed by what they consider the coach’s schoolmasterly style and tone.
‘In their view he is still the high school teacher: ever the smart-aleck, autocratic, comfortably convinced of the superiority of his own opinions, and no one should dare to criticise master van Gaal’s methodology.’
Van Gaal has always refuted these PE teacher comparisons but, watching him stood, hands planted on hips with an unchanging, unimpressed expression, as his United players are sent round the circuit, it’s hard to believe him.