Aguero suffered a hamstring strain against West Ham in October.
“I feel sure after the international break he will be better,” he said.
“He’s getting better but I don’t know. We don’t want him to have a setback but he’s getting better.”
Aguero’s fellow striker Jesus has returned to training before Tuesday’s Champions League tie with Olympiakos.
Manchester City is top of Group C after two matches, following victories over Porto and Marseille.
Spaniard Pep said it is harder to get out of the group stages now than it was 10 years ago.
“The teams are better, there is more money everywhere, a lot of clubs are buying players and important managers,” he said.
“It is really tough. It doesn’t matter where you go, you know you have to face quality.”
However, Guardiola wants the quartet to take responsibility for trying to secure City’s first Youth Cup trophy since the 2008 team that included Mee, Trippier, and Sturridge.
“If they are here, they can look to the important players to win the game,” said Guardiola.
“I prefer them to have the experience to play in the final, to have the responsibility of having to win and bring the cup back to Manchester.”
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