"He was held overnight and released under investigation - without charge - late on Monday and will not join the team in London.
"Hales, who was with Stokes on Sunday night, did not train this morning and has returned voluntarily to Bristol today to help Police with their enquiries.
"You will understand that we cannot offer further detail at this stage but will provide any updates when we can."
A statement from Avon and Somerset Police appealed for witnesses to "a disorder in the Queens Road/Clifton Triangle area at around 2.35am on Monday.
"A 27-year-old man was found to have suffered facial injuries and was taken to the Bristol Royal Infirmary for treatment," the statement continued.
"A 26-year-old man was arrested on suspicion of causing actual bodily harm and has since been released under investigation."
Strauss confirmed both players remain available for Ashes selection when the selectors meet later today.
The incident could not have been timed any worse for England. Tomorrow they announce the Ashes squad and one of their most high profile players, Stokes has been involved in a nasty off-field incident. On an Ashes tour the players are under greater scrutiny than on any other assignment and Stokes will be treading a fine line if he lands himself in trouble again.
He was sent home from an England Lions tour to Australia for breaking team curfews in 2013 and landed himself in further trouble with the England management on a tour to West Indies when he broke his hand punching a locker.