"A young lad can't ask for any more than facing someone like that," he said. "You have to be on your game every time you have a training session otherwise it turns into a nightmare.
"It's horrible when he runs at you but if you do well against him it is a great confidence booster.
"It is also fantastic for your concentration levels. If you can do a decent job against him every day then you can do a decent job against anyone."
Simpson will play tonight against Carling Cup opponents Coventry: "I have never played at Old Trafford, so to have the opportunity of making my United debut there is a really big thing."