Germany international Bastian Schweinsteiger is set for an indefinite spell on the sidelines as persistent knee problems have limited the Bayern Munich midfielder to only a few individual training sessions since the World Cup.
Ahead of the tournament in Brazil, Schweinsteiger had been nursing a knee injury which ruled him out of the DFB-Pokal final in May.
But the midfielder brushed away all fitness concerns to become a key player for Joachim Low's World Cup winners, most notably in the final against Argentina, where he played the full 120 minutes despite a head injury suffered in extra time.
However, according to German tabloid Bild, which headlined "Fear for Schweinsteiger" on their front page on Monday, the midfielder went through the past few months only with the help of injections to ease the pain in his knee.
"Basti has played with problems already last season, and also in Brazil. Currently he does nothing," Pep Guardiola told reporters on Saturday.
Asked about the duration of the midfielder's absence, the Catalan coach added: "You'd have to talk to [club and Germany doc Hans-Wilhelm] Muller-Wohlfart about this. He told a paper [in an interview directly after the World Cup] that he is set for a six-week spell on the sidelines, and thus he is injured, can't train. I don't count on him in the next weeks."
While Schweinsteiger featured for Bayern in the final match of their recent U.S. preseason tour against the MLS-All-Stars, he has been limited to only a few individual sessions since then.
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The latest setback comes at a bad time for Bayern, who are seeking a defensive signing with Javi Martinez out for up to seven months after picking up an anterior cruciate ligament injury last week.
Elsewhere there was better news for Bayern, with Holger Badstuber making his long-awaited comeback from injury.
Badstuber, 25, returned to action on Sunday 624 days after an ACL tear put a temporary end to his career, featuring in Bayern's 4-1 win in the first round of the DFB-Pokal at Preussen Munster.
"I'm delighted I got to play, I really enjoyed it and we won, so it's been a good day," the Germany international told reporters after the match.
"We have seen his quality and his personality," Guardiola said of the defender, who made his first appearance under the Catalan's regime at the club.
Meanwhile, Borussia Monchengladbach's 18-year-old midfielder Sinan Kurt has told Bild that he hopes to join the Bundesliga champions in the coming days.
The midfielder, who has drawn comparisons to Marco Reus, has been the subject of a transfer row between Bayern and the Foals in previous weeks, and hopes that the clubs can reach an agreement over the next 14 days.
"My decision in favour of Bayern stands," he said on Monday. "I am convinced that an agreement can be reached. Obviously, those weeks right now are wasted time for me."
The youngster was not called up to Gladbach's first team following the dispute which started in May 2014, and currently keeps fit with the club's reserve team.
"I have always kept [sporting director] Max Eberl in the loop. That's why there is nothing I could blame myself for," he said.
Monchengladbach had accused Munich of poaching an underage player, and had also hit out at Kurt for his attitude to Bayern's interest.