The FA confirmed the injury via a statement.
"During tonight's training session Theo Walcott dislocated his right shoulder after falling on the pitch," said the FA statement.
"Theo was taken to hospital, where he has had the shoulder put back into place.
"Theo will return to the team hotel and a decision will be made in the morning by the medical staff as to when Theo can fly home.
"Arsenal's medical staff were advised of the injury soon after the incident."