Police were called to Southgate Street at around 2.30pm today, Tuesday (April 4).
The victim, a man aged in his 30s, sustained a suspected stab wound to his shoulder area and was taken to Gloucestershire Royal Hospital for treatment, where he remains.
Meanwhile, a 31-year-old man from Gloucester was arrested in connection with the incident and remains in police custody for questioning.
A knife was also recovered at the scene and police cordons are currently in place outside WHSmith.
Gloucestershire police are not looking for anyone else in connection with the incident at this time.
Any witnesses, or anyone with information about the incident who has not yet spoken to police, is asked to call 101 quoting incident 252 of April 4.
Alternatively, you can submit information online, here – https://tinyurl.com/4abtem4u