Inaki Williams sent Athletic into a sixth-minute lead at Nuevo Estadio de Los Carmenes, but the match was stopped in the 17th minute due to a medical emergency in the stands.
It has since been revealed that a supporter of the home side has tragically lost their life, which led to the game being postponed, and it will now be rearranged for a later date.
"La Liga joins the pain of the Granada family and wishes to convey his condolences to the family and relatives of the Granada fan. Rest in peace," read a post on X from La Liga.
Meanwhile, Granada sent their "sincere condolences" after the tragic incident in their La Liga affair.
"We want to send our most sincere condolences to the family and friends, as well as to the entire Granada family. The match between Granada CF and Athletic Club, suspended after the death of a supporter of our Club," read a post from Granada's official account on X.
Barcelona were also among the clubs to take to social media in the aftermath.
"FC Barcelona expresses its deepest condolences to the loved ones of the fan who passed away during the game between Granada and Athletic Club. Rest in peace," read a post from the club on X.
Granada entered Sunday's clash off the back of successive defeats to Alaves and Real Madrid, with a difficult campaign to date leaving them inside the relegation zone.
The team are next due to be in action against Celta Vigo on December 16, which will be their penultimate contest before the campaign enters a winter break.
Athletic, meanwhile, were looking to make it three straight wins in all competitions on Sunday, and they will also be back in action next weekend against Atletico Madrid.