Vicente del Bosque has confirmed Hector Bellerin will replace Dani Carvajal in the Spain squad for Euro 2016 if the Real Madrid defender is forced to withdraw due to injury.
Carvajal picked up a muscle problem in Madrid's Champions League final win over Atletico Madrid on Saturday and is doubtful for the tournament in France.
Bellerin, meanwhile, made his Spain debut in Sunday's 3-1 win over Bosnia-Herzegovina and will remain with the squad until there is clarity about Carvajal's fitness.
"It all depends on what the medical staff say about Carvajal's fitness," Del Bosque said at a news conference.
"Bellerin will stay with the squad until we know the extent of Carvajal's injury.
"I also considered [Villarreal defender] Mario [Gaspar], but we have to remain consistent and bear in mind this training camp was in order to prepare for the Euros. That's why Bellerin will stay with the squad."
Del Bosque fielded a young team against Bosnia-Herzegovina as he was still without the Real Madrid, Atletico Madrid and some Barcelona players, but he was nonetheless pleased with his side's display as they prepare to try and retain their crown.
"We felt comfortable in the first and were in control with Bruno Soriano and Cesc Fabregas," he added.
"Even though we had a man more following their red card, we were less in control after the break. We did not take advantage of the fact they were down to 10 men.
"I am very happy with the youngsters, though. They will all return to Spain on Monday, except Bellerin. I then have 48 hours left to announce the final squad."