Sterling has scored 13 goals in 41 games in all competitions this season with Guardiola rotating his squad amid a congested fixture schedule. He scored 30 goals in 51 games in the 2019-20 season.
The 26-year-old said this week he was still enjoying his football in a "weird" season where the form of Gabriel Jesus, Phil Foden and Riyad Mahrez has limited his game time.
"The trust with Raheem is intact," Guardiola told reporters before Saturday's FA Cup semi-final with Chelsea. "... The only reason he has played less is because there's Gabriel sometimes or Phil or Riyad and they are at a top level.
"But his confidence? He has to have it. I can't give the players confidence, they have to have it for themselves. For me giving them confidence is to select them."
Despite the dip in form, Sterling is on course to add to his medal tally with City - who are still competing on four fronts - and Guardiola said the forward is still a vital player.
"I've said many times what we've done over these incredible years, with the amount of titles and breaking records in the process... Raheem is key," Guardiola said.
"But people talk about the past... about the quadruple. I couldn't care less. I care about today's training session."
