Fort, 18, has made 10 appearances for Barcelona during the 2024-25 campaign, with his last league outing coming against Real Betis on December 7.
However, a hamstring injury, which he suffered during a training session, has ruled the right-back out of what is a huge match at the top of the La Liga table on Saturday night.
"H. Fort has a strained hamstring in his left thigh and is out for today's match," read a statement from the club, but it is unclear how long the Spaniard will spend on the sidelines.
Barcelona will return to action after the winter break against Barbastro in the Copa del Rey on January 4, and it is believed that the teenager has a chance of featuring in that contest.
Fati returns to Barcelona squad vs. Atletico
There is some positive news on the injury front, though, with Ansu Fati being cleared to feature.
The 22-year-old has been missing for the last month due to a thigh injury, and his return will hand head coach Hansi Flick another option in the final third of the field, with Lamine Yamal missing due to an ankle problem.
Marc-Andre ter Stegen and Marc Bernal remain long-term absentees, while Andreas Christensen is also missing despite the Denmark international recently returning to first-team training after a long-term Achilles issue.
Ronald Araujo is once again in the squad, with the Uruguay international recovering from a hamstring operation, but it remains to be seen whether he earns his first minutes of the campaign against Atletico.
Barcelona squad vs. Atletico Madrid:
Pena, Szczesny, Astralaga; Cubarsi, Balde, Araujo, Martinez, Kounde, Garcia, Martin, Dominguez; Gavi, Pedri, Torre, F Lopez, Casado, Olmo, De Jong; Torres, Lewandowski, Fati, Raphinha, Victor
Written by
Matt Law