Gary Roberts' future at Port Vale could be in doubt after the club confirmed they are investigating a "serious breach of club discipline".
Vale have said they will not comment further due to the "ongoing and sensitive nature" of the investigation.
Roberts was suspended for two weeks in September and placed on the transfer list by manager Micky Adams after arriving at training unfit for duty. The 24-year-old has not started a league game since serving the suspension.
A statement on the club's official website said: "Port Vale can confirm the club is currently conducting a full investigation following a serious breach of club discipline by midfielder Gary Roberts.
"Due to the ongoing and sensitive nature of these enquiries, the club will not be issuing any further statement at this time."
Roberts, who joined Vale in July 2010, left each of his three previous clubs - Crewe, Yeovil and Rotherham - following discipline breaches. Since his suspension three months ago, he has started two FA Cup ties and made two substitute appearances in League Two.