Story updated 20:30 EDT
The incident happened during training at the Red Bull Arena in New Jersey ahead of United's friendly clash with the MLS All-Stars. The Mexican striker spent the night in hospital and is now resting at the team hotel.
A club spokeswoman told ManUtd.com earlier on Wednesday: "Chicharito sustained a mild concussion during training on Tuesday night. We have taken all the necessary precautions, which included an overnight stay in hospital."