Manchester City striker Sergio Aguero will not feature in this weekend's Barclays Premier League game at Aston Villa.
Aguero scored twice before being withdrawn after 86 minutes as City thrashed Manchester United 4-1 at the Etihad Stadium.
No injury was indicated at the time and nothing seemed untoward when he was then rested for the midweek Capital One Cup win over Wigan.
But Pellegrini has now revealed a problem and does not want to take the chance of playing Aguero at Villa Park on Saturday.
Pellegrini said: "Aguero finished the last derby in the last play with a small pain, I think it was nothing important but I think it was a risk for him to play three games in the same week.
"We will leave him for next Wednesday but he will be absolutely fine."
Playmaker David Silva, who has missed the last four games with a thigh strain is also not fit to return at the weekend but will be assessed ahead of the Munich game.
The European champions visit the Etihad Stadium on Wednesday in the second round of games in Champions League Group D.
Pellegrini said: "We will see in the week."
Pellegrini insisted the looming game against Pep Guardiola's Munich would not affect the players' thinking for the trip to Villa.
City laboured in a goalless draw at Stoke immediately prior to their last Champions League outing against Viktoria Plzen a fortnight ago.
Pellegrini had made six changes for that game and Potters boss Mark Hughes suggested City may have paid the price for prioritising the wrong game.
"We know it is a strong team playing at home. We need to play a very good game if we want to win and we need to win away now.
"We have lost one away and drawn the other, for different reasons.
"It is in the past so I don't continue talking about those games but tomorrow we have the opportunity to win against Aston Villa.
"It is very important for us to reach the first position of the table."
City have enjoyed an outstanding spell since that Stoke result, opening their Champions League campaign with a comfortable win over Plzen and then thrashing United and Wigan.
In the process they scored 12 goals and the fluid attacking style Pellegrini promised when appointed, even after 10 changes against Wigan, was much in evidence.
Pellegrini feels the team are getting close to playing in the manner he wants.
He said: "If we repeat what we did against Manchester United, very near.
"But all the games are different, performances are different, the squads are different.
"The important thing is we see the same team but with different names."
They may now have to make way again but Pellegrini expects all of his players to be able to slot in seamlessly when called upon and does not anticipate problems keeping everyone happy.
He said: "For me that is the least problem. The problem for managers is when you don't have players to make rotation or to play every week. That is not a problem for me.
"All the players understand it is mature players that we need, an important amount of players.
"I always said two in each position because we have a lot of games to play from now until the end of the year."
City's performances in their last three games, most notably against United, have earned considerable plaudits but Pellegrini is unwilling say whether he has the Premier League's best squad or not.
He said: "We are just starting the year so it is difficult in this moment to say who is the strongest squad.
"I think we have a very good squad and we will try to win all we play."