By Sam Lee
Aguero was stretchered off during Argentina's opening World Cup qualifier with a hamstring injury at the start of October, and has missed City's last seven matches.
And Pellegrini says that while the 27-year-old cannot play 90 minutes, he confirmed he will start against the Reds because Wilfried Bony, the club's only other recognised striker, is currently injured himself.
"Maybe it's difficult for him because [it's] too many days without playing," Pellegrini reflected when asked how Aguero will slot back into the team after a lengthy absence.
"I don't think that he's ready to play 90 minutes, or play two or three games in a week, so it's very important for Sergio to... he must evaluate during the game how many minutes he must play.
"He must start in one game, he must start on Saturday because we don't have Bony so it's important for the team to be with Sergio."
Aguero has suffered similar injury-enforced lay-offs in each of his seasons in the Premier League, and Pellegrini admitted it is hard for any club to prevent their players picking up muscle problems.
"We always try to manage those kind of things but it's very difficult to manage," he said.
"Not only in our team, I think a lot of teams have important players injured for different reasons... because the tempo is too high or because we play too many games, but we always try to manage in the best way."
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The City boss also caused confusion when he suggested Samir Nasri could be out for four or five months despite the player posting on Instagram this week that he will be out for three months.
"Vincent has a problem in his calf," Pellegrini said. "I hope that next week he will be fit. The calf is a difficult muscle, you never know how much he needs but I hope that next week he will be OK."
On Silva, Pellegrini added: "It’s a long injury, it’s not a muscle injury but the ankle. For different reasons he cannot be 100 per cent fit and if the player is not comfortable I think that he cannot play.
"He’s a player that we need, especially [now] that we don’t have Samir Nasri for four or five months, but I hope that, like Vincent, next week he can be okay."
Pellegrini may well have included the period that Nasri had already missed through injury before he sustained a tendon problem in training this week, as he had not featured since a substitute appearance against Bournemouth in October.
"Samir has a tendon injury in his right leg, so he must now have surgery," he explained. "It's an important injury. It was done in training and I think that he will be a long time out."
Fabian Delph, however, is fit to feature against Liverpool despite leaving England duty with an injury.
"He doesn’t have any problem, he worked the whole week after he returned from the national squad and he’s in the squad list for [Saturday]," said Pellegrini.