The Red Devils took a first-half lead at Craven Cottage through Christian Eriksen but were pegged back by a Dan James equaliser, only for teenage substitute Garnacho to claim all three points at the death with an explosive run and finish.
After some early season teething problems and attitude issues, the Argentine is now starting to establish himself in the first team, having also netted against Real Sociedad and bagged a pair of assists against Aston Villa in the Carabao Cup.
But Ten Hag feels the World Cup has come at the worst possible time for Garnacho and could be a big disruption to the momentum he was building – something the coaching staff will work hard to avoid over the coming weeks.
Asked about the 18-year-old’s latest dazzling cameo, Ten Hag said: ‘It would be weird if I said I knew that [he would have that impact] before. It’s a little bit the feeling that you have, you also need an eye for it. But sometimes I’m wrong as well!
‘But in this case we had a discussion with my coaches and I saw his improvement in the last months, and you could see his potential, and for me it was at a point to bring him in.
‘This shows the real talent, and what real talents can do, but for him there is still a long way to go. He has to keep his feet on the ground. The whole team does, but him especially.
‘He must do much more investment, because he will be recognisable for everyone so it’s much more important every time to confirm it. Big players know that, young players don’t know.
‘Now it’s a four-week break, that’s already a danger for him because he’s now got momentum, but now it’s cut. It’s a cut in the season.
‘So we will see how he comes back, we have to manage it, manage it with him, but when his attitude is good I am certain he will have an impact.’
Asked to expand on what he meant by the World Cup being a danger, Ten Hag continued: ‘The danger is four weeks of no games. He could lose focus, less investment.
‘It’s only when he’s staying in the same attitude that he’s been working with the last three, four, five weeks that the process will keep going and his progress will keep going. If not, it goes the other way around.’
MORE : Erik ten Hag defends Scott McTominay substitution and bemoans big Manchester United ‘mistake’
MORE : Louis Saha tells Manchester United starlet Alejandro Garnacho how to avoid becoming another Macheda or Januzaj
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