Del Bosque named his squad for the Euro 2016 qualifying clash with Ukraine and a friendly against Netherlands on Friday, selecting Chelsea's Diego Costa and Juventus striker Alvaro Morata as his only two forwards.
And Del Bosque believes it is becoming increasingly difficult to find world-class Spanish players in the country's top flight.
"We do have reliable goalscorers, but we are seeing in the Spanish league a lot of good players in important positions in their teams who are foreigners," he said.
"And on the other hand, our two main forwards [Morata and Costa] are not playing in Spain."
Spain host Ukraine next Friday before facing Netherlands four days later.
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