McDermott admitted on Thursday that he was still on the lookout for new players despite adding three players to his ranks this month.
Reading have monitored Aspas' progress since the Spaniard helped Celta achieve promotion last season with an impressive record of 25 goals in 37 matches.
The 25-year-old has made the step up to the Primera Division with ease this term, starring for Celta in what has otherwise been a tough return to the top flight for the Galician club.
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."