Quinnell rejoined the Scarlets in the summer on a two-year contract
Scarlets forward Gavin Quinnell has lost the sight in his left eye after an incident in Llanelli's 27-19 Welsh Premiership 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 to the Welsh Rugby Union (WRU) following the match at Pandy Park.
Gwent Police are also investigating an an allegation of assault.
"We received a report on Tuesday, 5 October of an allegation of an assault which occurred at Cross Keys Rugby Club on Saturday afternoon," said a police statement.
"A man received injuries for which he has received treatment. We are working with Llanelli Rugby Club, Cross Keys Rugby Club and the WRU and enquires are ongoing."
The Scarlets released a joint statement on Thursday on behalf of Quinnell's family.
It said: "It is with a huge disappointment and regret that today we can confirm that our Scarlets player Gavin Quinnell has received a conclusive report from medics that he has permanently lost his sight in his left eye.
"Naturally, the Quinnell family are all shocked and devastated and have asked to be given time and space to come to terms with the news and allow them to concentrate on giving Gavin their full support and attention.
Our thoughts and best wishes are entirely with [Gavin] and his family
Scarlets chief executive Mark Davies
"Gavin and his family have also asked the Scarlets to express their gratitude for the numerous messages of support and the heartfelt wishes they have received from the rugby community across the world and from supporters of the Scarlets.
"The family would like to add that Gavin is coping well, given what he has been through and they are all very proud of the way he is handling the situation.
"It is very sad news for all those connected with Llanelli rugby, the Scarlets family and rugby as a whole and all our best wishes and thoughts are with Gavin.
"The Scarlets will continue to offer Gavin and his family all the support they require going forward. "
A WRU statement confirmed a citing complaint had been received, but said: "The process is now in the hands of the WRU disciplinary panel in accordance with the Union's rules and regulations."
Cross Keys have so far refused to comment on the matter.
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 on Monday.
"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 after four years away from Llanelli - two years at Worcester followed by two years at Italian Super 10 side Viadana.
The 6ft 7in, 21st back-five forward, who is son of former Wales international Derek, and brother of Welsh internationals Scott and Craig.