Zinedine Zidane has confirmed Isco suffered a shoulder injury during Real Madrid's 2-1 Champions League semi-final win over Bayern Munich.
Isco made way at half-time for Marco Asensio, who went on to net a 57th-minute winner after Madrid left-back Marcelo cancelled out Joshua Kimmich's opener late in the opening period.
Speaking to television reporters after the match at the Allianz Arena, Zidane conceded the game-changing switch was largely a matter of necessity - and not one for which he could take too much credit.
"Isco had a shoulder problem, he did not feel comfortable from the start, so we changed him at the break," he said of the playmaker, who is central to Spain's plans at the World Cup. "We hope it is not too serious.
"With Isco being injured, you have no other choice than to change him. Asensio scored [but] you can't say it's my coaching because I replaced an injured player."
Zidane had little doubt Isco's international colleague knew how to grasp the big occasion.
"Asensio knows what he has to do with the ball. I don't tell him much about that, just a few things defensively," the Madrid boss said at his post-match news conference.
"We can play better, yes, but we can be happy with the game."
It is the sixth consecutive match Madrid have won against the German giants in the competition, keeping them in the hunt for a third title on the bounce.