The post, accompanied by a pointing-hand emoji and a white heart, quoted Psalm 145:17-18: "My God, you always keep your promises and you do everything with love. You are always close to those who call on you sincerely."
The message came just hours before Argentina were due to face Cape Verde in the last 16 of the 2026 World Cup, a match in which Fernández could start.
Real Madrid issued a statement on Friday, reported by Marca, saying they had made no approach, direct or indirect, to sign the midfielder and ruling out any move this summer.
The statement followed recent reports linking Real Madrid with an interest in the Argentinian.
Javier Pastore, Fernández's agent and a former Paris Saint-Germain player, spoke to Marca at an event organised by the AFA in Miami.
Asked about a possible move to Real Madrid, Pastore did not rule out a departure from Chelsea.
"Right now the player is calmly focused on the national team, he's playing in a World Cup, he's very close to reaching the last 16... He's only thinking about that, and we're looking at possibilities to leave Chelsea, but there's nothing firm or confirmed with any club," he said.
Pastore also addressed Fernández's known fondness for Madrid.
"He has a lot of friends there, he's very close with Julián Álvarez, and in the end whenever they can spend time together, they're together there. I also live in Madrid. Every time he's travelled, it's been to see me and sort out work matters, but beyond that — who doesn't like Madrid?" Pastore said.
Fernández's future remains tied to Chelsea for now, with Real Madrid publicly closing the door on a deal this summer.