The Primera Liga champions slipped to fifth after Sunday's 4-3 defeat to Sevilla at the Bernabeu, nine points behind the Catalans, and have lost three of their last four matches in Spain's top division.
Dutch winger Arjen Robben will miss Saturday's game at the Nou Camp because of his red card against Sevilla and key players such as centre back Pepe, midfielder Ruben de la Red and striker Ruud van Nistelrooy are still out injured.
"It's impossible to win at (Barca's) stadium," Schuster said at a news conference.
"They are devastating. I think it is their year," he added. "We will try to put on a good show. We won't be able to do more than that."
To compound Schuster's problems, the club announced on Monday that Mali midfielder Mahamadou Diarra would be out for six to nine months because of a right knee injury and winger Royston Drenthe limped out of training, also with a knee problem, putting him in doubt for Wednesday's Champions League tie against Zenit St Petersburg and the Barcelona game.
Defeat, or even failure to win, against Barcelona would ratchet up the pressure on both Schuster and club president Ramon Calderon, who endured a stormy general assembly meeting in Madrid on Sunday.
Angry club members reiterated criticism levelled at Calderon and sporting director Predrag Mijatovic for failing to bring in top-quality players.
Mijatovic put the defeat to Sevilla down to bad luck and said the team had shown in the second half that they had the desire and the ability to put the recent poor run behind them.
"This team is strong and can come back," he said on the club's website (www.realmadrid.com). "The league is very long."
Schuster said Real had been on the brink of winning Sunday's match after fighting back from 3-1 down at the break to level at 3-3 but Robben's sending off had scuppered their chances.
"We showed character but it was not to be," the German said. "We did some bad things during the match but I also saw some very good things, especially in the second half."
In one piece of good news for Schuster, midfielder Wesley Sneijder returned to training on Monday after he missed the defeat to Sevilla with a muscle strain.
