During the transfer window, City managed to secure the services of Julian Alvarez from River Plate but he would not join the Premier League giants until the summer but Guardiola may yet still look to sign another striker.
Man City also missed out with several attempts to sign England striker Harry Kane from Tottenham Hotspur.
"I think the club needs a striker, definitely," Guardiola said ahead of Sunday's derby at home to Manchester United.
"You say we play fantastically well without a striker because we are winning. When we are not winning, you say we need a striker."
City lead the table by three points from Liverpool but have an inferior goal difference compared to Jurgen Klopp's side.
Guardiola's team have netted 64 times in 27 games so far this season, seven fewer than Liverpool.
Aguero, who scored 260 goals for City, left at the end of last season to join Barcelona and the club failed with a succession of bids to sign Kane as his replacement.
City's Brazilian striker Gabriel Jesus has usually featured on the wing this season while they sold Ferran Torres, another forward who can play up front, to Barca in January.
"(You say) 'how do these guys play without a striker? In the Premier League you have to play with a striker'," said Guardiola.
"So, we need a striker, I think the club is going to try."