Quinnell rejoined the Scarlets in the summer on a two-year contract
Scarlets forward Gavin Quinnell has lost the sight of his left eye after an incident in Llanelli's 27-19 defeat at Cross Keys.
Quinnell, 26, had surgery at Newport's Royal Gwent Hospital after Saturday's game, but his sight could not be saved.
Llanelli and the Scarlets have made a formal citing complaint following the Welsh Premiership match.
Gwent Police are also investigating an "an allegation of assault", according to the Western Mail.
Cross Keys have so far refused to comment on the matter.
"The Welsh Rugby Union has received a citing complaint from Llanelli RFC with regards to an incident that took place during the club's Principality Premiership match at Cross Keys RFC on Saturday, 2 October," said a WRU statement.
Our thoughts and best wishes are entirely with [Gavin] and his family
Scarlets chief executive Mark Davies
"The process is now in the hands of the WRU disciplinary panel in accordance with the Union's rules and regulations."
Llanelli RFC and the Scarlets say they have issued the WRU with a full written report and DVD footage in line with citing procedures.
"Everyone at the Scarlets and Llanelli RFC was devastated to hear about Gavin's injury and our thoughts and best wishes are entirely with him and his family," said Scarlets chief executive Mark Davies.
"We are grateful for the prompt action and outstanding care from emergency services and the Royal Gwent hospital and we all hope that he recovers well.
"We have lodged a formal complaint and the matter is now in the hands of the WRU and their formal disciplinary process."
Quinnell returned to the Scarlets on a two-year deal in the summer.
The 6ft 7in, 21st back-five forward had been away from Llanelli for four years.
The son of Derek and brother of fellow Welsh internationals Scott and Craig, had spent two years at Worcester then the last two at Italian Super 10 side Viadana.
The match report on Llanelli's website contained the following statement.
"In a poor advert for rugby, the match was further stained in the 30th minute when the popular, in-form Gavin Quinnell suffered a bad eye injury."