Kompany, the influential captain and centre-back, is poised to return to action after 10 games out with a thigh injury as City travel to West Brom in the Barclays Premier League in midweek.
The Belgian has been missed for his leadership, organisational and defensive skills and will be gladly welcomed back at The Hawthorns, even though Pellegrini believes his deputies have fared well.
Pellegrini said: "Kompany is in the squad list and he is travelling with the team.
"Vincent is a very important player. He is a very good defender and, of course, we need him.
"He is also the captain of the team and he will normally be in the 11 starting.
"We have other captains but all the team is happy with the return of the captain.
"But I repeat, we don't have as many problems in defending as the scores say and the results say.
"I think we have the third best defensive record in the Premier League.
"In the last five (domestic) games just Sunderland have scored one goal (against us). In all the others we have had clean sheets.
"So the other defenders can do it as well, but Vincent is always an important player."
Yet it can be argued that some of City's exhilarating home performances - including 7-0 and 6-0 thrashings of Norwich and Tottenham respectively - have masked defensive deficiencies.
These have particularly come to light away from home and City have lost at Chelsea and Sunderland during Kompany's absence.
They were also beaten at Cardiff in August in another game Kompany missed.
In all, City have lost four out of six away games - a statistic which contrasts sharply with their 100 per cent home record and is threatening to undermine their title challenge.
They will hope to start putting that right this week as the West Brom game is followed quickly by a trip to Southampton, although Pellegrini maintains the approach to all games has been the same.
The Chilean said: "Against Aston Villa, against Cardiff and against Sunderland we made individual mistakes that decided the match but we didn't give the home team five, six, seven (scoring) options each game.
"It is important to concentrate more. It is more an aspect of concentration and intensity during the whole match.
"This week we play two games away before we play against Arsenal here at home, so I hope we will be the same team we are here in those two games this week."
City's inability to replicate their home form on the road is puzzling but West Brom, who also have a good reputation for attacking football, will want to test their resolve further.
Pellegrini said: "They are a very strong team - a mixed team. Sometimes they play long, sometimes they want to build up short.
"They are a strong team in the air and a very strong team defending, so we need to play a good match.
"I saw the games they played against Chelsea in London and the draw at home against Aston Villa and they are a difficult team."
The potential return of Kompany is timely, with fellow central defender Matija Nastasic out with a calf injury. Playmaker David Silva and striker Stevan Jovetic also remain on the sidelines with similar problems.
The other major selection issue in recent weeks has concerned the goalkeepers, but Costel Pantilimon seems likely to be retained ahead of England's Joe Hart.
Hart did play in last week's Champions League tie against Viktoria Plzen, but Pantilimon has been the man in possession since the start of November and impressed against Swansea on Sunday.
Pellegrini said: "Joe Hart continues to be the number one of England. He is a very good goalkeeper.
"But Pantilimon has played seven games - four in the Premier League in which he has conceded just one goal - so that is also important for the team.
"They are two important goalkeepers. I trust in both of them. At the moment I am playing Pantilimon, but you saw the other day when Joe Hart played he did very well."