Southend are investigating three players for an alleged breach of club discipline procedures prior to Saturday's defeat at Morecambe.
The conduct of Liam Dickinson, Kane Ferdinand and Ryan Hall in the team hotel on Friday night has lead to the investigation, but it is not known what the incident in question was.
The Shrimpers lost the League Two game 1-0 and manager Paul Sturrock was not told what had happened the previous night until after the defeat.
"The manager and the board of Southend United require their players to behave professionally at all times in the best interests and success of the club," a club statement read.
"It is now an internal matter and no further comment will be made."