Anthony Martial may have left Manchester United tour without permission - sources

LOS ANGELES -- Manchester United's tour of the United States has hit more problems after Antonio Valencia was sent home with an injury while confusion reigns over whether Anthony Martial received permission to attend the birth of his son, sources have told ESPN FC.

Valencia has returned to Carrington with a suspected torn calf suffered during the draw with San Jose Earthquakes in Santa Clara on Sunday.

The right-back will miss the remaining four warm-up games and will be a doubt for the opening day of the season against Leicester at Old Trafford on Aug. 10.

Martial has also left United's Los Angeles training base to be with girlfriend Melanie Da Cruz.

It was initially thought the Frenchman had been granted leave by manager Jose Mourinho but United were unable to confirm that was the case on Wednesday.

If the 22-year-old has left before seeking permission it will further damage a relationship with Mourinho that, sources have told ESPN FC, is already strained.

Martial wants to leave the club this summer and, according to sources, Mourinho is willing to cash in as long as he is not sold to another Premier League club. Chelsea and Tottenham are among those interested.

The departures of Martial and Valencia is a further blow to Mourinho who has cut a frustrated figure in the United States.

He has already admitted he is worried about the first two games of the Premier League season against Leicester and Brighton because so many of his senior players are still on holiday following the World Cup.

He has been forced to take a young squad to the U.S. and has said his team could lose by some "not beautiful numbers" when they play AC Milan, Liverpool and Real Madrid.

Mourinho also has mounting concerns, according to sources, that he will not get any more new players before the Aug. 9 deadline.

He wants two new signings -- with sources saying they are a centre-back and a right winger -- but has said repeatedly "there is a difference between what I want and what will happen."

So far this summer he has sanctioned deals for Fred, Diogo Dalot and Lee Grant.

At a press conference at UCLA on Tuesday, Mourinho refused to answer a question about whether his squad, as it stands, is good enough to win the Premier League title next season.