The ‘Strictly Come Dancing’ star and his brother were attacked in the Nakatcha nightclub in Nantwich, Cheshire, shortly after 2am on 27 December.
Curtis, 22, was left needing knee surgery while 24-year-old AJ suffered bruising to his face, arms, body and legs.
A spokesman for Cheshire Police said four men, three aged 22 and one aged 24, were assaulted by a group of males in the club and were all taken to Leighton Hospital for treatment, but have since been discharged.
They’re now urging anyone with information on the attack to come forward, confirming that they are in the process of reviewing CCTV from the night.
Detective Inspector Claire Jesson said: “This was a serious incident and we are committed to doing all that we can to trace the people responsible and bring them to justice.
“Inquiries in relation to the incident are ongoing and officers are currently examining a large amount of CCTV footage from the nightclub and speaking to a number of witnesses who have come forward.”
A 20-year-old man from Crewe was arrested on suspicion of assault following the incident but has been released under investigation.
Speaking earlier this week, AJ said his brother risked his own career to try to shield him from the blows.
“He was thinking of both my dancing career with my legs and my TV career with my face,” he said. “He tried to protect me and in doing so saved my life and my legs from danger.”
Curtis had been due to appear on the Irish version of ‘Strictly’, ‘Dancing With The Stars’, but had to pull out due to his injuries.
Anyone with information should can contact police on 101, online or anonymously via Crimestoppers.