Aguero has been struggling with a knee injury and Kompany has been out since January after suffering a calf problem in the FA Cup fourth-round victory at Stoke.
"Sergio is in Argentina but he will come back on Sunday," said Mancini. "Vincent is not in our plans. But I think he will be ready for the Newcastle game, like Sergio."
However, the City boss accepted Kompany's injury has proved rather more serious than initially believed.
"It is difficult," said Mancini. "Vinny is a really important player for us and now it is 45 days he has been out. It is a big problem."
It hardly helps City this weekend given they are facing Everton, who have proved a difficult opponent to overcome in recent times.
The Toffees have won five of the last seven games between the pair, and drew at the Etihad Stadium earlier this season.
"Every game against Everton is very hard," said Mancini. "They are a top team who always play at 200 per cent. They have good players and a good manager."