The 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.
Pellegrini had previously stated that he hoped to welcome Kompany back for next weekend's derby against Manchester United.
But it now seems he could be back in action sooner than expected although Pellegrini was at pains to stress he would not take any unnecessary risks with the City captain's fitness.
"Vincent has worked with us normally for the last two days," Pellegrini said at a pre-match press conference at the Doosan Arena.
"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."
Without Kompany, City have kept clean sheets in their last two games leading Pellegrini to play down the impact of the Belgian's absence.
He added: "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."
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 or 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 for Saturday's 0-0 draw 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."