According to James McCabe, the incident occurred following a dispute between his father and coach Patrick, and the staff member at the Edgbaston Priory Club over the use of practice courts on Monday morning.
Writing on Instagram, James McCabe, who is ranked 234, described the altercation as a "serious police-reported player/coach safety incident at the tournament venue.
"My account is that he was followed, physically handled by a staff member, and left in pain afterwards."
West Midlands Police said in a statement: "We received a report of a man being assaulted at a venue in Sir Harrys Road, Birmingham on June 1. No arrests have been made and enquiries are ongoing."
McCabe, who lost his first-round match, added on Wednesday morning that his father had gone to hospital as a result of the incident.
The tournament is the first of the British grass-court season and features events on the second-tier ATP Challenger and WTA 125 tours.
It is run by the Lawn Tennis Association and a joint statement from the governing body, the ATP and Edgbaston Priory Club, read: "There is an ongoing investigation being led by Edgbaston Priory Club with support from the ATP and LTA in relation to an incident during the Lexus Birmingham Open on Monday, June 1.
"This incident involves an allegation made against a member of Edgbaston Priory Club staff by a player's coach and is currently being reviewed by an investigating officer.
"We will be making no further comment whilst the investigation is ongoing."
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