Pace is certainly the 22-year-old’s biggest weapon, with his speed across the pitch helping to bring him to the attention of those at Old Trafford.
A £15 million ($19m) transfer from Swansea over the summer has been the reward for James’ rapid progress over recent years.
He is now starring on a Premier League stage, with his efforts in 2019-20 having marked him out as one of the more consistent performers in a United side which has struggled to find such qualities at times.
James is also a key man for his country, despite his lack of experience, and the next coach he is about to face is all too aware of the threat posed by a player who is similar to Paris Saint-Germain star Mbappe when it comes to ripping through opposition defences.
Rossi said ahead of a crunch Euro 2020 qualifier for Wales against Hungary: “James is a player that is playing with a motorbike because he is really fast.
“I have never seen someone in the last period as fast as him, maybe Mbappe. He's unbelievable.
“If we leave him space to run he could be dangerous. This could be the key, but we work a lot on the defensive line and will try to give confidence to our players.”
Wales have to beat Hungary at the Cardiff City Stadium to give themselves a chance of securing automatic qualification for next summer’s European Championship.
Rossi’s side know that a draw will be good enough for them if Slovakia fail to overcome Azerbaijan.
He is, however, looking for his side to get on the front foot against Ryan Giggs’ troops and keep their fate in their own hands.
“We are trying to get the three points, I would never like to draw and give Slovakia the chance to go through to the Euros,” Rossi added.
“This is what I would want to avoid. This is not so diplomatic what I am saying, but it is the truth.
“We will do all our best in order to win, Wales will do the same, and I don't think this match could finish in a draw. I could not bet one pound on the draw.
“I will ask of my players, if they [Wales] are dragons, to be lions - and then we will see who will win.”
Tuesday is set to deliver the final round of Euro 2020 qualification fixtures, with the draw for the play-offs and group stage of next year’s event due to be held in Bucharest on Saturday.