Port Vale midfielder Gary Roberts is being investigated over a 'serious breach of club discipline'.
Roberts was on the bench for Vale against Hereford United last Monday at Edgar Street.
The ongoing enquiries are said to be of a 'sensitive nature'.
Roberts has already been suspended once this season after he failed to turn up for training on the Sunday following defeat by Shrewsbury the day before.
He was 'unfit to carry out his duties' said manager Micky Adams at the time.