Manchester City fear that Vincent Kompany will miss the next three Premier League matches owing to a groin injury he suffered in the home win over Newcastle United.

The captain is expected to return for the derby with Manchester United on 22 September and with Matija Nastasic not yet in full training following an ankle injury, Manuel Pellegrini has Joleon Lescott as his only fit senior central defender. The situation may accelerate City's desire to fill the gap, with Real Madrid's Pepe and Atlético Madrid's Martín Demichelis of interest.

Kompany was unable to have a scan on Tuesday owing to swelling so City will not discover the severity of the problem until the test is carried out on Wednesday afternoon. The prognosis is that he could be unavailable for up to a month. This would mean the 27-year-old missing Sunday's trip to Cardiff City, the visit of Hull City to the Etihad Stadium the following Saturday and the trip to Stoke City on 14 September – the first game after Belgium play Scotland during the international break.

The World Cup qualifier is on 6 September in Glasgow and it is understood that the Belgium team's medical department has been in contact with Kompany and the club to ascertain whether he will be available. While this is a match Marc Wilmots's side want to win to ensure their three-point lead over Croatia in Group A is maintained, the manager is anticipating being without Kompany for it.

Kompany's absence represents a significant blow to Pellegrini. Nastasic has been out since injuring an ankle at the Asia Trophy in July and though the manager stated on Friday Nastasic could rejoin training with the first team this week, he has yet to do so. Much depends on how the 20-year-old reacts when he does resume, with Pellegrini concerned about rushing him back.

With Micah Richards out for "weeks" owing to a hamstring injury, Pellegrini may ask the midfielders Gareth Barry and Javi García to play in defence at Cardiff as a temporary option or call on Dedryck Boyata, a central defender who has struggled to establish himself.