The 28-year-old Raphinha, who has not recovered from a leg muscle injury, joins a host of high-profile absentees, including Dani Olmo, Robert Lewandowski, Gavi and goalkeepers Joan Garcia and Marc-Andre ter Stegen.
With 10 players sidelined since August, Barca’s injury crisis has left their squad severely depleted ahead of one of the most crucial fixtures of the season.
Despite Raphinha's setback, the Spanish champions remain optimistic that they can count on key players Ferran Torres, Jules Kounde, Andreas Christensen and Frenkie De Jong, who all took part in Saturday's team practice.
"Any team would miss Raphinha, but the situation is what it is. He is injured," Sorg told a press conference.
"We'll see if Ferran (Torres) starts, we'll decide tomorrow. Jules Kounde also trained this morning and may play. I still have no idea about the starting eleven."
Torres left Spain's camp early with leg muscle fatigue, while De Jong missed three training sessions this week due to a illness and Kounde was forced out of the 6-1 win over Olympiacos in the Champions League in midweek after a blow to the leg.
The injuries further complicate the Catalans' selection headaches for the crucial encounter against Real Madrid, who sit two points ahead of second-placed Barca after eight games.
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Flick suspended
Sorg will take charge on Sunday with Barca manager Hansi Flick suspended after being shown a red card during the 2-1 win over Girona in LaLiga on October 18 for allegedly protesting against refereeing decisions in the dying minutes of the match.
Sorg acknowledged that 60-year-old German Flick's absence will be felt but insisted the team remains prepared.
"Flick will always be missed because he's one of the most important parts of the team," he said.
"I think to have Flick on the sidelines, because the players trust him, he gives them confidence - his absence does have an influence. But Flick is in a good mood, positive, motivated."
Despite the mounting challenges, Sorg expressed confidence about taking charge of the prestigious fixture.
Barcelona enjoyed four consecutive wins over Real in three competitions last season, putting 16 goals past them including a 4-0 rout at the Bernabeu and a 5-2 Super Cup final win.
"It's an honour to be on the bench leading this team. It will be a tough match and I hope we can show our strengths," said Sorg, who will face Real's new manager Xabi Alonso.
"Real have made progress from last year, they press high up the pitch, I think that's changed (from the previous term). You never know what can happen at the Bernabeu... We have to control our emotions and we’re ready.”