Nastasic sat out the midweek UEFA Champions League win over Viktoria Plzen after being withdrawn at half-time in last Sunday's 6-0 Premier League thrashing of Tottenham.
Pellegrini is reluctant to rush back the Serbia international, while Vincent Kompany will not be risked against Swansea on Sunday, despite his recent recovery from a thigh problem.
"Vincent Kompany is fit and he is not ready to play on Sunday but I think next week he will be without any problems," said the Chilean.
"Jovetic and Silva - I think they will play against Bayern Munich.
"Nastasic needs more time to recover - I think three weeks more.
"Rodwell is fit and can play this Sunday."
Goalkeeper Joe Hart returned for Wedneday's 4-2 win over Czech side, but it remains to be seen whether Costel Pantilimon will be preferred at the Etihad.
Pellegrini praised Hart's performance, but failed to reveal whether he will keep his place between the posts.
"Joe Hart, I think he played very, very well the other day," he said.
"He had a good performance. We trust a lot in him and we will see who will start on Sunday."
"All the players give me a lot of things to think about and that is my job.
"When they give good performances, it is very easy. Not difficult, easy."
City's slack defensive display in the 4-2 win over Plzen was greeted with dismay from Pellegrini, who admits his side must tighten up.
"In the last two game here at home in Champions League, both teams scored two goals. It is too much," he said.
"Especially in the last game - Plzen did not just score two goals but they had
"We are working every day in that sense.
"I suppose we will continue the same way we did against Tottenham - a very strong team with important players in attack and they didn't have any