The 21-year-old made his latest appearance in the pre-season during United's 4-0 win over Leeds United in Perth, Australia, on Wednesday.
Robson was on punditry duties for the match and he went into detail on the qualities which James brings to the table at United.
The former United midfielder was quick to highlight the Wales international's pace but he also identified his willingness to defend as one of his strengths.
In fact, Robson compared James to United great Ryan Giggs in that regard during an interview which was full of praise.
"He has been really impressive. He is really quick. He goes about his training really well," Robson told MUTV. "For me, if you want to be a really good player you have to train well and that lad does.
"He has a great attitude and he's not bothered if someone hits him with a hard tackle. He will get up and proceed with the game.
"He works back a bit like Giggsy. He was a great tackler and people never really mention that.
"If James keeps working hard and can score a few goals, he will be a great asset for the club."