With Chelsea and top Spanish sides reported to be interested in signing the player, McDermott appears to have been priced out of a move for the star, who is said to be valued at around £10million.
"I would be surprised if anyone could do that deal. It's an expensive deal and a difficult one for anyone to do," McDermott said.
"I've seen him play, our scouts have seen him play and he has had a couple of really good seasons.
"We know him - but it's a very difficult deal to do. Celta Vigo are a big club.
"The money that they are talking about on this player (Aspas) is a fortune.
"There would have to be some structuring to do on that - but we've never done a deal like that.
"The biggest deal that this club has done is £2.5million when we signed Emerse Fae and we sold him back for the same sort of money - the same with Greg Halford."