Celta Vigo striker Aspas replaced Diego Costa in the squad after the Atletico Madrid forward was released for personal reasons.
Aspas impressed as Spain beat England 2-1 at Wembley in League A Group 4 on Saturday.
Spain host World Cup runners-up Croatia in Elche on Tuesday and Aspas is poised to start again.
"You have an idea of what you expect from someone and after the training session he shows you that he's something else," Luis Enrique said.
"I recognise my error. I thought he had a good game, I saw him train well. I'm open to change. The team comes before anything else."
The coach would not reveal his line-up but said his players do not look tired after overcoming England.
Croatia's midfield boasts Real Madrid's Luka Modric, one of the three finalists in FIFA's The Best awards, and Ivan Rakitic, who worked under Luis Enrique at Barcelona.
However, the Asturian coach says Barca's Lionel Messi is still the best player in the world.
"If I talk about Croatia I would talk about Modric and Rakitic," he said. "If I have to talk about the best in the world, that's Leo Messi."
(Editing by Ed Osmond)
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