Jonny Evans and Gareth Barry among players under investigation by West Brom after incident during Spanish training camp
Four senior West Brom players were involved in "an incident" during the club's mid-winter training trip to Spain.
The Baggies announced on Friday that they have opened an investigation into the matter, with Jonny Evans, Gareth Barry, Boaz Myhill and Jake Livermore subsequently coming forward as the players involved.
The club say the quartet will be "subject to the full rigours of our internal disciplinary procedures", and that they will make no further comment until their investigation is completed.
Manager Alan Pardew said the players involved broke a curfew that had been imposed on them.
"It wasn't what we wanted. We've gone there to try to get ourselves ready and up for the run-in and this is obviously not ideal," he said.
"They broke the curfew and that's unacceptable and I feel a bit let down by that. It was a curfew on that evening and it was broken and that's all I'm going to comment."
He added: "As much as you want information and stuff, the club is clear it wants to investigate it properly and I think that's right. We just want to concentrate on the game now. Our fans will want to see us put on a performance."
The players also released a statement addressing the incident.
"We would like to take this opportunity to apologise to our team-mates, the Head Coach, the Club and especially the supporters for the events which have been the subject of widespread and negative publicity.
"We felt it important we identify ourselves as the players involved in an incident which occurred during the training camp in Spain this week out of respect for team-mates who otherwise could be implicated by association.
"We freely acknowledge and apologise for the break of curfew which we accept represented a breach of the standards of professionalism required of us as representatives of West Bromwich Albion FC.
"The Club has informed us that it will now conduct its own inquiry into the incident and we will co-operate fully.
"In the meantime, we would like to assure our supporters that this incident does not reflect the determination and resolve we possess to do all we can to recover a difficult season."
West Brom play Southampton in the FA Cup fifth round on Saturday.