The Citizens' bid to secure the services of Harry Kane failed in the transfer window but replaced him with the signing of Jack Grealish.
And having being without a striker for quite a long time after losing the club's all-time leading goalscorer Sergio Aguero to Barcelona, Guardiola believes his side lack 'weapon' like Ronaldo.
"Always I had strikers in my career," Guardiola said ahead of Saturday's trip to Chelsea.
"Like goalkeepers, strikers are the biggest specialist position. I played with Samuel Eto'o, Thierry Henry, (Lionel) Messi, (Robert) Lewandowski, Thomas Mueller, Sergio for a few years here.
"The club needs in the next years a striker. When it's not possible, it's not possible, we move on with the fantastic squad we have. "Strikers are strikers, but they are the most difficult players to take (from other clubs)," said Guardiola.
"We were privileged to have Sergio for many years. Unfortunately he was out injured last season and we survived without him. With him we knew we had something extra.
"We have two options: complaining or working with the exceptional players we have. "We don't have this weapon like United, Chelsea or Tottenham. We don't have the player to score 25 goals, we have to do it as a team."
Aside being without a striker, City have been scoring more goals in their previous games and have also been top-scorers in the Premier League for each of the past four seasons.
