The 29-year-old has been bailed pending further inquiries into the incident in Manchester on Sunday, PA quoted sources as saying.
Two hours after the alleged attack, the player was involved in a car crash and charged with drink-driving, driving while disqualified and having no insurance.
A Greater Manchester Police spokeswoman said: “At approximately 3.30am on Sunday April 29 a woman was assaulted at a nightclub on Barton Arcade, Manchester city centre.
“A 29-year-old man was arrested on suspicion of Section 47 assault.”
At 5.20am on Sunday, police were called to Sale, Greater Manchester, to reports that Pennant’s white BMW had been involved in a collision with a silver Audi.
The driver of the Audi was taken to hospital and treated for a minor back injury.
Pennant is due to appear at Trafford Magistrates’ Court on May 9 to answer the driving charges.