Manchester City manager Pep Guardiola said his side are now "in trouble" after Portuguese midfielder Bernardo Silva joined the club's lengthy injury list.

Silva, who signed a one-year contract extension last month which will keep him at City until 2026, was forced off before halftime in City's 3-1 home win over Red Star Belgrade in their Champions League opener on Tuesday.

City are already without key players Kevin De Bruyne, John Stones, Jack Grealish and Mateo Kovacic due to injury.

"He (Silva) didn't say anything at the end," Guardiola said. "I didn't speak with the doctors, but apparently, for the next games, he won't be able to play."

Premier League leaders City next host Nottingham Forest on Saturday, looking to make it six wins from six, but Guardiola is worried about the impact of having so many key players absent at the same time.

"We are in trouble but I am not going to say, 'Oh, we have a lot of injuries'," he told reporters.

"When we have five important players - really, really important players - injured, to sustain that for a long time will be difficult. But it is what it is."