The 29-year-old has been bailed pending further inquiries into the incident, alleged to have happened at the Circle Club on Sunday.
A witness told The Sun: "This girl started to have a real go at him saying, 'You've got a baby, you got my friend pregnant and now you are here with other girls’.
"Afterwards he was dragged outside. She was pretty upset with him."
The incident is alleged to have happened just two hours before Pennant was involved in a car crash, for which he was subsequently 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."
Pennant is due to appear at Trafford Magistrates' Court on May 9 to answer the driving charges.