The forward limped out of City's 1-0 win over Everton at the start of December and was subsequently ruled out for six weeks with strained knee ligaments.
Aguero's absence added to Manuel Pellegrini's problems in attack, with Edin Dzeko and Stevan Jovetic both spending time on the sidelines in recent weeks.
That saw City deploy James Milner in attack in some matches, but Jovetic did return in the 2-2 draw with Burnley on December 28.
However, the Premier League champions may soon be able to call upon Aguero again after he revealed he is back in training.
"I wanted you to know I've already started field work," he posted on his official Twitter account on Monday.
"Slowly but surely I'll be back at the right moment."
Even without Aguero, City have continued their impressive form in all competitions, with six wins in the seven matches.
The Argentina international has scored 19 goals in 21 appearances for City this season, including a stunning hat-trick against Bayern Munich in the UEFA Champions League to book his side's last-16 place.
Pellegrini will now hope the 26-year-old has no relapses to ensure he is ready for their two-legged clash with Barcelona in the knockout stages - the first match in Manchester on February 24.
