David Moyes's concerns over the strength of Everton's central midfield have been realised with Marouane Fellaini joining Darron Gibson on the sidelines with a knee injury.

The influential Belgian has been ruled out of the forthcoming World Cup qualifiers against Serbia and Scotland with an injury sustained at Wigan Athletic, and will also miss Everton's trip to Queens Park Rangers after the international break. Fellaini's prospects of facing Liverpool on 28 October rest on his response to treatment over the next fortnight.

The Belgian FA had stated the 24-year-old would be out for three weeks but Everton have not placed a timeframe on the recovery.

A statement from the Belgian FA read: "Fellaini suffered a small tear at the juncture of muscle and tendon in the knee. The injury was revealed during a scan. Fellaini was injured last Saturday during the match between his club Everton and Wigan Athletic. He will be out three weeks. It has been agreed with his club that he will rehabilitate in Belgium during this period."

Fellaini has been deployed in a more advanced role this season by Moyes but his absence, if only for the QPR game, underlines the manager's fear that central midfield could hinder Everton's prospects of competing for Champions League qualification.

The Everton manager has used Phil Neville and Leon Osman as his midfield pairing in recent weeks with the thigh injury Gibson suffered at West Bromwich Albion on 1 September proving more serious than initially thought. Moyes had hoped the Republic of Ireland international would be out for three weeks but, with the Merseyside derby a possible comeback date, has been almost two months without the 24-year-old.

Moyes attempted to sign the Belgian midfielder Vadis Odjidja-Ofoe on loan from Club Brugge on deadline day, only for Fifa to rule the paperwork had not been completed on time, and voiced concerns over his options only last week. "We are still short of central midfield players and, if you're talking about a squad to compete at the top end of the Premier League, I'm worried we are not going to have that level," he said.

The former Aston Villa midfielder Thomas Hitzlsperger has been training with Everton for several weeks with a view to a short-term contract and played for the under-21s at Norwich City on Monday.