Costa has refused to return to Stamford Bridge as he attempts to engineer a move to Atletico Madrid and was consequently left out of Spain's World Cup qualifiers against Italy and Liechtenstein during the September international break.
"Costa's summer has been unusual, strange, complicated – not just for him but for his club," Lopetegui told Spanish media. "He is still a Chelsea player. It's a complicated issue.
"Our hope is that he will resolve his situation as soon as possible and that he can compete, train and play, which is what he likes doing the most and what interests the national team.
"It's rather complicated that a guy who doesn't train and doesn't play can be with us, but that's all it is.
"He wasn't ready to play with us against Italy and Liechtenstein, that was the reality and what we had to deal with. That is the reason why he wasn't with us. He needs to train and play in order to be considered."
Costa last played a competitive fixture on May 27 - 116 days ago - as Chelsea were defeated by Arsenal in the FA Cup final.