Erik ten Hag told Manchester United's teenage winger Omari Forson that he would have been sent off against Borussia Dortmund in Las Vegas if there was VAR at the game.
Ten Hag substituted Forson 38 minutes into United's 3-2 defeat to the Bundesliga side at the Allegiant Stadium after he was involved in a flare-up with defender Julian Ryerson.
Forson kicked out angrily at Ryerson and was then booked for squaring up to Karim Adeyemi who stepped in to defend his teammate.
Ten Hag immediately told Antony to warm up and sent on the Brazilian star for Forson as his spat with Ryerson threatened to escalate.
The 19-year-old winner looked crestfallen to be subbed before half-time, and was consoled by Scott McTominay and Christian Eriksen as he walked towards the touchline where Ten Hag was waiting to give the youngster a lecture.
'When there is a VAR, he gets sent off,' said the Dutchman. 'He played a good game and the opponent gets annoyed with him, so that is a learning curve but don't take it into your own hands.
'You can't be the judge, you have to play football, you have to beat your opponent, you have to net and that is the best way to react.'
United started with a weakened team and took the lead through an excellent goal from Diogo Dalot.
But they conceded twice to Donyell Malen in 18 seconds before half-time and although Antony equalised early in the second half, Youssoufa Moukoko punished more shoddy defending with a late winner.
Ten Hag, who sent on a number of first-choice players after an hour, described the capitulation as 'unforgiveable'.
He kept the squad behind longer than expected afterwards before the team flew back to Manchester from Las Vegas after losing three of their four games on tour.
'There are no excuses,' he
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