The Argentina international has made three substitute appearances for the Catalan outfit since returning from a calf problem and scored his first goal for his new side against Real Madrid on Sunday.
Speaking ahead of Wednesday's clash with Rayo, Koeman has confirmed that the 33-year-old is now capable of taking to the field for the first whistle, having built up his fitness.
"Aguero is ready to have more time on the pitch, even if he isn't yet ready to play 90 minutes," Koeman told reporters. "He is ready, though, to start a match or to play the entire second half."
The South American arrived at Barcelona on July 1 but had to wait until October 17 to make his debut for the club, having picked up a calf issue in the early stages of August.
Blaugrana, who suffered a 2-1 loss in El Clasico last time out, are currently ninth in La Liga, six points behind division leaders Real Sociedad. body check tags ::