City conceded a stoppage-time equaliser that left them with a second consecutive draw and saw them lose ground in the title race to Arsenal, who are now six points clear after 20 games.
"We will see tomorrow (about Gvardiol) but it doesn’t look good for him or Ruben,” Guardiola told reporters.
“I didn’t speak with the doctor but if Ruben is out it is because he felt something.
"Have you seen the bench today? Four players from the academy and now we will have more. We don't have players."
City are already without central defender John Stones, who has missed the last six games due to a thigh injury, while Nathan Ake has also struggled with fitness issues.
Despite the injury problems, Guardiola was confident his side could compete if they believed in themselves.
"After what happened last season, if we stay strong we will find a solution and the spirit will be there," he said.
“If the spirit is there, we will be there.”
City will next host Brighton on Wednesday.