Manchester City captain Vincent Kompany is poised to return to action in his side's opening Champions League game against Viktoria Plzen in the Czech Republic.
The inspirational defender, who has not played since suffering a groin injury in the opening game of the season, has travelled with the squad ahead of the Group D encounter.
Despite that, Pellegrini said he will not take any unnecessary risks with his key defender.
Pellegrini, speaking at a pre-match press conference at the Doosan Arena, said: "Vincent has worked with us normally for the last two days.
"We will see if he is 100 per cent. If he is, of course he will play. We will talk with the doctor and decide.
"I think he will be 100 per cent, but if he is not he will not play.
"We have a very important match but we have other players if any are not 100 per cent."
Kompany was badly missed as City suffered a shock loss to promoted Cardiff in their second Barclays Premier League game of the season.
Since then they have kept two clean sheets but questions have been asked of their injury-hit defence, most notably in Saturday's goalless draw at Stoke.
He said: "Vincent is a very important player for us. He has been injured for about one month.
"But without Vincent, except for the game against Cardiff, the defence played very well. We have had three clean sheets.
"Vincent is very important but we have a squad. We have replacements for any player who is injured."
Left-back Aleksandar Kolarov, sitting alongside Pellegrini, delivered an even more positive assessment of Kompany's fitness.
Kolarov said: "Vincent is our captain and a very important player for us. Now he is 100 per cent and we are looking forward to playing with him."
City are anxious to get off to a winning start as they bid to finally make an impact in the Champions League at the third attempt.
City failed to win their opening games in either of their two previous campaigns, both of which ended prematurely at the group stage.
Pellegrini's previous record in the Champions League, having taken both Villarreal and Malaga to the latter stages, was one of the key factors in his appointment this summer and hopes are high of progress this time.
But the Chilean, who was celebrating his 60th birthday on Monday, said: "Of course we have to win this game. It is very important to start the group winning the first game.
"But the Champions League is never easy. If we think we have weak teams in our group we are making a big mistake.
"Plzen are a very good team. I know they are a team that have not lost in the last 13 games and are the champions in the Czech league.
"It will not be easy but we will try to continue to the last 16."
Pellegrini made six changes at Stoke, five of them tactical, and watched in frustration as his team failed to break down the Potters.
Stoke boss Mark Hughes suggested City may have paid the price for prioritising the Champions League trip but Pellegrini insisted there were many reasons for his selection.
He said: "I changed some players last Saturday for a lot of things, not only because we have the Champions League.
"It is very important to play Champions League and I also know we have the derby next Sunday.
"But it is different playing Tuesday and Sunday, than it is Saturday-Tuesday.
"It was also a week when most of our players played in their national squad. I think that was the best team we could play against Stoke."
City have now put that game behind them and Kolarov wants to ensure the players give Pellegrini the perfect birthday gift.
The Serbian said: "I think the best present will be three points. We will give 100 per cent to make a present for him and one for us."