United’s £73 million signing missed out on a place in England’s World Cup squad after an inconsistent first half of the campaign under Erik ten Hag.
Sancho also missed United’s last four matches before the World Cup break due to illness.
The 22-year-old also confused supporters last week when he deleted all of his posts on Instagram and blacked out his profile.
But ahead of United’s winter training camp in Cadiz, Spain, which is due to begin next week, Sancho is already working on his sharpness as he was spotted training with Rosmalen in the Netherlands.
It’s understood that Sancho is working with Dutch coaches who have been personally recommended by Ten Hag.
Rosmalen wrote on social media: ‘We hope you had a pleasant training with us! You are always welcome to train with us and have a good time.’
Meanwhile, Alejandro Garnacho has credited Ten Hag with his impressive performances for United before the season was halted.
‘Erik Ten Hag is a very good manager and, above all, he’s a great person,’ Garnacho told United’s official website this week.
‘He always pays very close attention to us all, and helps us a great deal, especially the young players.
‘I’ve had to keep working hard until that moment came where I was given my opportunity. For the moment, I’m making the most of the opportunities he’s giving me.
‘I don’t want to take a backward step from here, I’d like to appear regularly in the team and keep going in the same way.’
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