Michu was tipped to be in the frame for a call-up, having scored 16 goals for the Welsh club this season.
He misses out along with Chelsea's Fernando Torres, with coach Vicente del Bosque naming a 21-man squad.
As for Michu's absence, Del Bosque said: "It's left a little bit of a bad taste in the mouth not to call up someone who deserves it. But those who have been named also deserve it.
"We recognise his worth and his goals in the Premier League but we couldn't find a space for him at the moment.
"The same thing happened with Iago Aspas. I'm honest and don't hide anything. In the position which Michu plays there is great competition with five or six players."
Del Bosque's two main striking options next week will be Alvaro Negredo and David Villa who is currently not a regular in the Barcelona side since returning from a broken leg.
As for Torres, Del Bosque added: "Torres is one of our most experienced players at international level but neither could we find a space for him now.
"Villa's case is not comparable with anybody. I'm not worried that Villa is only playing a little.
"Every time he's gone out he's done well. There's a lot of competition in his team. His case is unique.
"He had a very serious injury but he's played a very important part in our recent successes."