Silva emerged as an injury doubt for the derby after he was left out of the squad that travelled to Ukraine for his side's final Champions League group match against Shakhtar Dontesk on Wednesday. Guardiola later explained the Spain international had picked up a minor knock after scoring the winning goal in his side's previous fixture against West Ham United.
Jose Mourinho wasn't buying that, however. After seeing Arsenal striker Alexandre Lacazette start against his side last Saturday despite his manager ruling him out, the United boss suggested Guardiola was attempting to pull a similar ruse.
Guardiola was adamant there was an injury but having spoken to the player and team doctors, he has confirmed Silva has been cleared to feature in the first Manchester derby of the season.
"He's going to play," Guardiola told a press conference.
"The doctor told me in the beginning of the week there was a doubt about him playing but today he arrived and said he felt really good, so he's going to play."
City have two further concerns this week however with both Vincent Kompany and Fabian Delph left out of the squad that lost to Shakhtar. The skipper was expected to start at the heart of defence in City's final group game on Wednesday but instead Fernandinho dropped back to partner Eliaquim Mangala as the Premier League leaders suffered their first defeat of the season.
Guardiola explained post-match Kompany did not play because he "didn't feel good" while Delph missed out after taking ill at the start of the week.
Nicolas Otamendi and Kyle Walker meanwhile both made the trip to Kharkiv but spent the evening on the subs' bench. Both will come back into the first-team for Sunday, but the City boss is unsure at this stage if the other two members of his planned back-four will be ready.
"Vincent Kompany felt something and was not comfortable before Wednesday's game and that is why he could not play," Guardiola said. "Delph was sick, he vomited and had a fever and that is why he couldn't play.
"Kyle Walker and Nicolas Otamendi were the only guys who could play who didn't. Today is their day off, so I don't know the other players' condition, but tomorrow I will check.
"He [Kompany] knows his body better than anyone. "He felt something and couldn't play against Donetsk. I wanted him to play to get rhythm before Old Trafford."
Kompany's absence would act as a decisive blow for Guardiola with John Stones already ruled out with a hamstring injury. Mangala and 20-year-old Tosin Adarabioyo, both who played the full 90 minutes midweek, are the manager's only other available natural centre-halves.
Should Delph be unavailable it will also present Guardiola with a major problem at left-back. The former Leeds United starlet, who is normally deployed in midfield, has been providing cover for Benjamin Mendy, who is unlikely to play again this season.