Both players have been prolific for much of the season, scoring 49 between them, but injuries have brought a halt to their output in recent weeks.
Pellegrini could combine the pair for this weekend's FA Cup quarter-final against Wigan in the hope of building momentum for the Champions League trip to Barcelona next Tuesday, when City must overturn a 2-0 deficit.
Pellegrini said: "In that moment (earlier in the season), it was very productive for the team - and I hope in the future it can be again.
"But in other moments when Sergio was injured, Negredo played very well at that time. (Edin) Dzeko and Negredo, Dzeko and Sergio have also done it. It's important to have important strikers."
Aguero, City's top scorer this term with 26, returned to action after a five-game lay-off with a hamstring problem to play 58 minutes in the Capital One Cup final last weekend.
Pellegrini said: "I also think it was very useful for Sergio to play the 50 or 60 minutes with his national squad.
"He played the same amount of minutes in the final so every match he will improve."
Negredo has enjoyed a fine first season with the club but has now gone six games without a goal since taking his tally to 23 with a double in the League Cup semi-final second leg win at West Ham.
The Spaniard suffered a shoulder injury in the same game and is still to recover his sharpness.
Pellegrini believes his performances have probably been affected by fitness and a subsequent loss of confidence.
He said: "Maybe it is a little bit of all of those.
"It starts with a problem with his shoulders. Strikers also live from the goals they score.
"But I trust absolutely that Alvaro will return to his normal performance. He will continue scoring goals, the same as Edin."
The lack of sharpness could be a concern for Pellegrini but, on the other hand, the players - and especially Aguero - could be fresher for the run-in as a result of their lay-offs.
Pellegrini said: "Of course if you don't play every week you are fresh in the last part of the season but that freshness must also be linked with his performance.
"Maybe not playing so many matches is not good for a player.
"You never know what is best but I think Sergio will always be very important to us, whether he's fresh or not."