When Marcelo was replaced in the 74th minute of a Champions League clash at the Santiago Bernabeu, the role of Blancos skipper came up for grabs.
As the longest-serving Madrid player still left on the field, the honour was expected to be bestowed upon Isco.
He had, however, been jeered by certain sections of a disgruntled fanbase during a shock 3-0 defeat and opted against donning the armband when Marcelo tried to pass it to him.
The Brazilian defender told reporters afterwards: “He told me I had to give it to Carvajal.
“I don't know what the reason for that was.”
Marcelo had been captaining Madrid in the absence of Sergio Ramos.
Isco was next in line, but he happily passed duties on to Carvajal.
The Spainish international claims that decision had already been agreed prior to kick-off, with there no public showing of petulance from a man who had skippered the side against Melilla in the Copa del Rey.
Carvajal told Real Madrid TV: “I feel very proud and honoured to have worn the armband in a competitive match.
“I'd like to thank Isco, because by rights he should have had it, as he signed for the club a few days before me.
“He wore it against Melilla, and he said to me then that next time, if the circumstance came about again, he would let me have it. I'm grateful to him for that, because it was a really nice gesture.”
Carvajal added to La Sexta: “He [Marcelo] didn't know about it, that's all there was to it.”
Real will be hoping to avoid causing more controversy when they return to action on Saturday against Rayo Vallecano.
It remains to be seen whether Isco will play any part in that contest, with the 26-year-old having struggled for game time under Santiago Solari.
Goal has revealed that his future in the Spanish capital has now become a subject of much uncertainty, with the player seemingly unsettled and the Blancos board reluctant to persevere with potentially disruptive influences.