"I've always wanted to test myself against the best and Vidic is classed as one of the best defenders in the Premier League - so I'm looking forward to that. I watched United in the FA Cup against Southampton in the third round when my mate Ryan Smith gave Vidic quite a hard time.
"Hopefully I can turn and run at him. Vidic didn't really cope that well with Ryan doing that."
West Brom boss Tony Mowbray believes Simpson has already established himself as the club's most potent threat despite having not started a Premier League game for Arsenal before moving to Albion.
He said: "Jay had not played in the Premier League before he came here. I am sure his aspiration is to go and play for a top-four team, play for Arsenal and be a regular for them.
"He has got a way to go on his journey, and when he came in, he was a young boy who never really registered for Arsenal in terms of playing in their Premier League side. He comes into our club and is undoubtedly the most talented forward we have got.
"That shows the gulf and class difference, where he is not in and around the Arsenal first team and yet comes here and looks the most likely centre-forward on the pitch. That is just down to class and quality.
"He is a lively boy with good technique, has pace and is direct, is positive, plays without fear.