Aguero has wasted little time getting back into his goalscoring groove after a month on the sidelines, coming off the bench to strike in his first two comeback matches.
Despite missing eight games with a calf injury suffered in December, the 25-year-old already has 21 goals to his name this season.
It says much for free-scoring City's attack that he was hardly missed during his absence, with Alvaro Negredo and Edin Dzeko maintaining the prolific output, but Aguero's return was still enthusiastically welcomed.
Manager Manuel Pellegrini hailed Aguero as the world's third-best player behind Lionel Messi and Cristiano Ronaldo before his injury and Zabaleta does not disagree.
Right-back Zabaleta said: "I'm really happy to see him back.
"He needs to get back to his best in a physical way because he's been out for a month, but he took 30 seconds (actually 50) to score a goal when he came back against Blackburn and, on Saturday, 20 minutes.
"It's so easy for him.
"Every time we talk about good strikers, Sergio is one of the best in the world.
"Probably Messi and Ronaldo at the moment are in a different world, but I think Sergio is one of the best and we are very lucky to have him in the team."
Nevertheless, it is clear City have the firepower to cope without Aguero, if necessary.
City have now scored 103 goals this season as they chase glory in four competitions.
Negredo has been as prolific as Aguero, having also scored 21, while Dzeko has netted 16 and Yaya Toure 14.
Negredo was the only one of that trio not to score in Saturday's 4-2 win over Cardiff in the Barclays Premier League, but he might be excused after bagging seven in his previous four games.
Zabaleta said: "In football you have to be prepared for when someone important is missing or suspended.
"It was great to see him back again but Edin and Negredo have been doing really well without him.
"Sometimes the competition between them is all about scoring goals.
"It doesn't matter who plays, it's all about doing well for the team."
Zabaleta also rates City's talismanic midfielder Toure among the game's elite.
The Ivorian is enjoying an outstanding season by his own high standards.
Zabaleta said: "He's scored 14 goals this season and for a central midfielder that's fantastic.
"Yes, he's probably one of the best. He's a complete player."
Yet for all the attention on City's attack, Zabaleta did admit frustration that they conceded twice to bottom-of-the-table Cardiff, ending a run of three successive clean sheets.
The 29-year-old said: "It's nice when you see we've scored so many goals but as defenders we talk about clean sheets.
"That's something we need to improve. At this stage of the season, to keep a clean sheet in games is crucial.
"We know that any time we can score, so it's important to be a balanced team."
Aguero will expect to be fully match-fit to go head to head with that other Argentina star, Messi, when City take on Barcelona in the Champions League next month.
Zabaleta is friends with the pair of them but has not spoken to Messi since the draw for the last-16 of the Champions League was made last month.
He said: "No I haven't, but maybe I will speak to him a few days before that game. We will see."