Jonny Evans
Evans set to join United's injured list.Getty

Manchester United's defensive crisis could be about to worsen amid concerns Jonny Evans will miss a month of action through injury.

Louis van Gaal is already without his first-choice option of Phil Jones, who faces another three weeks on the sidelines after suffering a hamstring injury while on international duty.

Tyler Blackett, who had been ever-present in the Dutchman's starting XI this term, will also be unavailable for the visit of West Ham United this Saturday after being shown a straight red card in the 5-3 defeat to Leicester City.

And while the return of Chris Smalling to the United squad briefly eased van Gaal's concerns, the club are set to lose Evans due to a fresh ankle injury, according to the Daily Telegraph.

The 26-year-old Northern Irishman was forced off just half an hour into the humiliating loss to Nigel Pearson's side on Sunday, where he was replaced by Smalling, who was making his third appearance of the season.

Evans returned to the dugout for the second half of the game wearing a protective boot on his right foot. He underwent a scan on the knock on Tuesday, with initial reports suggesting the centre-half will mid out of action until mid-October at the earliest.

United face home games against West Ham and Everton before the second international break of the season. They return to action against West Brom on 20 October, a possible return date for Evans.

Without three of his options at centre half, van Gaal is likely to have no choice but to move Marcos Rojo inside to play next to Smalling and hand Luke Shaw his Premier League debut at left back for the visit of West Ham.

Shaw, a £27m signing from Southampton, suffered a hamstring injury a week before the new season started. The 19-year-old returned to the bench for games against Queens Park Rangers and Leicester City but has yet to make a competitive appearance for his new club.