Manchester City reached the quarter-finals of the Champions League for the first time despite a lethargic second leg goalless draw against Dynamo Kiev.
City, 3-1 up from the first leg, were in control of the tie but lost both centre-backs Vincent Kompany and Nicolas Otamendi to injury early on.
Jesus Navas hit the post with a low drive in the second half and Yaya Toure struck straight at the goalkeeper.
“Vincent has again a muscle injury in his calf, the same problem he has had before,” said Pellegrini.
“He will miss at least three quarters of the rest of the season.”
The Belgium international, 29, has started just 13 games in the Premier League all season and has had 14 calf injuries since signing in 2008.
Kompany is set for scan on either Wednesday or Thursday, with Pellegrini stating that “always with muscle injuries it is a minimum of one month”. Naija and Bet
The defender will certainly miss Sunday’s derby against Manchester United, and is likely to miss City’s Champions League quarter-final first leg on 5 or 6 April.
In all competitions this season, Manchester City have conceded a goal every 156 minutes with Kompany on the pitch and every 70 minutes without him on the pitch.
Pellegrini, who will leave the club in the summer to be replaced by current Bayern Munich boss Pep Guardiola, said reaching the last eight for the first time is an important milestone in the evolution of Manchester City.
“It’s a very important achievement for the club because before we couldn’t do it,” said the Chilean.
“It’s not normal to play Barcelona twice as we have the last two years and before that we didn’t qualify. We’re a club that is growing and to get this far is important.
“In this round of knockout you must be able to play this kind of tactical game and I’m happy in that sense and I’m sure we will continue to improve in this competition.”
City will learn who their opponents will be in Friday’s draw, with Barca the side to avoid according to Pellegrini.
“When you are at this stage, all the teams are difficult,” he said.
“I keep having in my mind that the team that it is better than all the other teams is Barcelona. I think all the other teams are at a similar level.”
Despite finally advancing to the last eight of Europe’s premier club competition, former England defender Rio Ferdinand was unimpressed with City, who won the League Cup earlier this season but are 12 points behind leaders Leicester in the Premier League.
“I think they’ve gone backwards,” he said”Have they got any real chance of winning the Champions League? No. They’re further down than at any time since the money was injected.”
