Costa had not featured for Spain since a World Cup qualifier against Macedonia on June 11 and missed the team's final four qualifiers because of a dispute with Chelsea.
Chelsea striker Alvaro Morata was one of the big names left out of the latest Spain squad, and La Roja's head coach has now explained why he was snubbed.
"There are players that are not on the list that still have chances to go to the World Cup".
"This was the right time for them to come due to their form and the current situation in the squad", Lopetegui said at a news conference.
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Yet Lopetegui can count on Diego Costa, who was called up on Friday for the first time in more than nine months having been overlooked in that period because he couldn't play with Atletico Madrid until the team's transfer ban from Federation Internationale de Football Association ended in January.
Spain boss Julen Lopetegui has revealed that Morata's chances of making the World Cup are not over, but he has sent out a major message by axing him and he must surely now be feeling the pressure.
"There are many players who could be called up, who deserve it and haven't been included because we have to keep the squad to a certain number".
"I'm sure he's going to have an extraordinary end to the season and will have every chance to be with us".
He said: "I think we have to try to do both". And the Leicester game shouldn't be seen as just a chance for Conte to give some game time to his fringe players - the FA Cup is Chelsea's last opportunity for a trophy this season.
"Diego is back with us because he has returned to play but this does not guarantee him a [World Cup] place", Lopetegui said.