Top scorer Aguero is back in training after six matches out with a calf injury and is expected to return to the first team later this month.
City have an interest in "two or three" unnamed players, meanwhile, but Pellegrini's priorities this month lie elsewhere with a Capital One Cup semi-final against West Ham and an FA Cup replay against Blackburn on the agenda.
He said: He said: "For the moment, there is no news. Of course if we bring a new player here to City it is because he is a very good player.
"In this squad we have a high level, so if we want to improve we must try to buy an important player.
"It is not our first concern and we are not in a hurry to make a decision. We are just seeing two or three things but nothing important."
Of Aguero's return he said: "It is very good news. All players recovering from injuries is good news, especially a player as important as Kun Aguero."
Stevan Jovetic will miss the first leg of City's semi-final against West Ham on Wednesday, still troubled by an untimely hamstring injury which has denied him the chance to stake a first-team claim in Aguero's absence.
Pellegrini said: "For the player it is always very bad news when he cannot play, but I think he is a very important player.
"He was the best choice to replace Kun Aguero when Kun got injured, but things happen and we must try to be optimistic for the future and suppose Stevan will play in the second part of the season."
Micah Richards, meanwhile, is over his hamstring injury but needs "to work a little more" before he is available, according to Pellegrini.
Meanwhile Pellegrini expects his under-fire West Ham counterpart Sam Allardyce to bounce back from his weekend FA Cup humiliation.
A weakened Hammers side were thrashed 5-0 by Sky Bet Championship side Nottingham Forest on Sunday, increasing the pressure on Allardyce.
West Ham are 19th in the Premier League having not won in that competition since November but Pellegrini is reading little into that form ahead of their midweek meeting.
Pellegrini said: "They had an awful result but I don't think they played with their best XI. They played with young players.
"I am absolutely sure tomorrow will be a very different game to what they played on Sunday.
"I think that in this job as a manager - in any club, in every part of the world - you are always under a lot of pressure.
"When the results are not the results the club wants, maybe sometimes it can be more nervous, but I think he is doing very good work in West Ham so I don't think he will have any problems."
Nevertheless, City, with their formidable home record, will be expected to win comfortably and take a big stride towards a place in the final.
That would put City, and Pellegrini, in clear sight of a first trophy since he took over.
With City also in contention in the Premier League and still in the Champions League and FA Cup the season has much potential, but Pellegrini is not looking too far ahead.
He said: "We are not thinking about the four trophies. We are just thinking about winning the next game we have to play.
"Tomorrow is one of the two games of the semi-final of Capital One, it is very important and we play here at home.
"We are going to have to have a very good performance to try to win against West Ham.
"After West Ham, we will think only about Newcastle. We are not thinking about the trophies, only the present."
After some rampant displays at home in recent months - notably scoring seven against Tottenham and six against Arsenal - Pellegrini knows how important another strong display could be.
He said: "It is very important to play the first leg here at home.
"Tomorrow we will try to win and if we can score more than one goal at home it will be very important also for the second leg."