Javier Hernandez will be out of action for at least a fortnight after sustaining an injury during training yesterday.
The 23-year-old striker was taken to hospital after suffering concussion while preparing for Man Utd's game against the MLS All Stars on their US tour.
A club spokesperson confirmed: "Chicharito sustained a mild concussion during training last night. We have taken all the necessary precautions, which included an overnight stay in hospital. The manager will give further updates in due course."
Manager Alex Ferguson said: "He got concussion in training and we dealt with that. We took him to hospital, he had a scan, it was all clear. He is back in the hotel. He is in his room and will be out for a couple of weeks.
"He would never have been available for [the game with] Barcelona [on Saturday] anyway because he has just come back from his break after the Gold Cup. He will travel with us though. He is OK for that."
After the US tour, United face rivals Man City in the Community Shield on August 7. Their Premiership campaign kicks off with an away fixture at West Brom on August 14.