City have not yet booked their place in the next round and face a tough test at Borussia Monchengladbach on Wednesday, with Toure currently ineligible to play in the tournament.
However, after the veteran midfielder scored twice on his first Premier League appearance of the season against Crystal Palace on Saturday, Guardiola hinted Toure could be added to City's squad for the knockout rounds.
"Of course now he's not able to play on Wednesday, or in the last game against Celtic," Guardiola said.
"If we are able to qualify in the Champions League, after, I will sit with my staff and we will decide who are the best players to help us to achieve in the Champions League games."
Guardiola insisted he does not regret freezing out Toure following a spat with the player's outspoken agent, Dimitri Seluk, but accepted he does sometimes make errors of judgement.
"I'm here to take decisions," Guardiola said. "Maybe I make mistakes, but I have to take decisions and I respect that all the people cannot agree with me. That happened.
"I spoke in the last month, many times with Yaya because he was my player with Barcelona, I know him very well. So I know how he is like a player.
"As a player there is no doubt [about his quality]. If there was a doubt he would not be here.
"He is another guy to compete with our midfield players and increase our level."