Manchester United striker Javier Hernandez spent the night in hospital after suffering mild concussion during a training session on Tuesday.

The problem did not become apparent until United had finished their session at the Red Bull Arena but Sir Alex Ferguson and his medical team were sufficiently concerned to send Hernandez to hospital, where he remained under observation for the remainder of the evening.

It is believed the 23-year-old Mexico striker, who only joined up with his team-mates on Monday, should be released at some point on Wednesday, with Ferguson due to give an update after the game against the Major League All-Stars, which Hernandez was not scheduled to be involved in anyway.

Although the extent of his concussion will determine when he will be allowed to play again, there must be some doubt as to whether the striker, who scored 20 goals last season, will feature against Barcelona in the concluding game of United's five-match tour in Washington on Saturday evening.

"Chicharito (Hernandez) sustained a mild concussion during training last night," said a United spokeswoman.

"We have taken all the necessary precautions, which included an overnight stay in hospital.

"The manager will give further updates in due course."