Rafael faces a race against time to be fit for United's first league match against Swansea

Manchester United defender Rafael has returned to England for treatment on a groin injury that could sideline him for the start of the Premier League season.

The Brazilian full-back was training with the first team squad ahead of their friendly match against Italian side Inter Milan when he sustained the injury.

The 24-year-old, who was omitted from the Brazil World Cup squad, will return to United's Aon training facility where he will recover and prepare for the new Premier League season.

Depending on the severity of the injury, Rafael could be out of action for at least three weeks if the injury is a strain, which means he could miss United's curtain-raiser against Swansea on 16 August.

A statement on the official United website confirmed the Brazilian had returned to Manchester.

"Rafael has returned to Manchester to continue treatment on the groin injury sustained in training in Denver," it said.

"As he was unlikely to participate in the remaining tour games, returning to the Aon Training Complex affords the best overall option for his recovery in time to continue pre-season preparation when the team returns."

The injury gives United manager Louis van Gaal a defensive headache ahead of the new campaign.

The Dutchman has been using a 3-5-2 formation reliant on two wing-backs and has so far used winger Antonio Valencia on the right where Rafael would usually play.

It is likely the 62-year-old will keep faith with Valencia in that position for United's final two matches of their American tour against Inter on Wednesday and Real Madrid on 2 August.

But as United look to make an immediate impact in the Premier League, van Gaal faces having to shuffle his defensive pack.