Captain Vincent Kompany will miss Manchester City's final Champions League group game - against Borussia Monchengladbach - with a calf injury.
The 29-year-old has been sidelined with the problem since early November.
Striker Sergio Aguero, defender Martin Demichelis and midfielder Samir Nasri are all injured too.
City have already ensured their place in the last 16, but could overtake Italian side Juventus at the top of the group with victory.
Juventus - two points clear of City and with a better head-to-head record - play Sevilla away in their final group game.
As it stands, second-placed City risk being drawn against Real Madrid, Barcelona and Bayern Munich - who are all leading their respective groups - in the first knockout stage.
"It is important for us to do our task, to win the game and then see what happens with Juventus," City manager Pellegrini said.
"The most important thing is to qualify, but once you have done that you have to finish at the top, so there are not too many players to rest, maybe one or two."
City have kept only two clean sheets in their last 10 Premier League games having kept six in a row prior to that, but Pellegrini denied that their defensive slump was down to skipper Kompany's absence.
"Over the whole season, there are a lot of games that we play without our important players," he said.
"Last season we played the last six games without Vincent Kompany and we won all six and kept four clean sheets.
"Against Stuttgart [in a pre-season friendly] we played with Vincent Kompany and we conceded four goals.
"It is not just one player."
Gladbach lost their first five league games of the season, but have won eight of the next 10 to climb to third behind leaders Bayern Munich and Borussia Dortmund.
