Costa is already amongst the goals for Atletico after waiting to complete his bitter departure from Chelsea.
Lopteguei stated: "Diego Costa has been important for us. It 's been a big journey without him competing and now, fortunately for him, for his team and for us he is competing. And doing very well. We are happy and hopefully it stays that way. The final photo call will be in May and it makes it more difficult for us to decide.
"He is a type of player that we have not hidden that we like, that we like, as we have always said we'd bring him when he has been able to come.
"I am not surprised because we know the mentality that he has, his ambition.
"He has prepared very well and is at a very good level, now he has been injured but it seems it will not be important and that he will return quickly to compete."
On Real Madrid midfielder Isco's selection battle, Lopetegui added: "He has not played in the last few games but the season is very long and there is a long way to go We fully trust Isco and the rest of his teammates.
"I am concerned with the little he plays, as with other players. But surely he'll play again."