Although the Valencia deal came very late in the window, Koeman says a potential move for the 26-year-old Ecuador international had been on the agenda for some time.
"We know he can play like a nine, or behind a striker. We have different options with Enner, and that is good to have.
"He will bring that competition that all players need. Now, including Valencia, we have seven players for the three front positions in the team, and you need that - it is a long and difficult season.
"They need to give competition and the best ones in my opinion will start. They need to accept that and fight for the best chance to play."