Jonny Evans, Gareth Barry, Jake Livermore and Boaz Myhill have apologised for breaking a West Brom curfew during a training camp in Barcelona.
The quartet have come forward following a statement earlier on Friday in which the club said they were investigating an "incident" during their stay in the city, which has left boss Alan Pardew feeling "let down".
According to Reuters, four West Brom players were questioned by police over the alleged theft of a taxi this week.
In a statement ahead of their FA Cup clash with Southampton this weekend, club captain Evans, Barry, Livermore and Myhill said they "felt it important we identify ourselves as the players involved in an incident in Spain".
They said: "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."
Sky Sports News understands the team had dinner at a restaurant in the city before watching that evening's Champions League fixtures on Wednesday, but afterwards four players went unaccounted for and missed a midnight curfew.
On Friday a source from the Catalan police force Mossos d'Esquadra told Reuters: "There were four people who wanted to go out in the city centre.
"Everything was closed so they got a taxi to a McDonalds by the Barcelona port. At some moment the driver left the car for some reason and the four people took control of the car.
"They eventually returned it to their hotel and we got a call from the receptionist saying they had parked outside the hotel. This happened at 5.30am. The taxi was returned to its owner at 8am.
"The four people were not arrested but they are under investigation. They were called into the police station about a crime of vehicle theft and made statements. Their statements have been sent to an investigative judge."
To add to a tumultuous week for the club, Pardew had his jacket stolen on Tuesday night in Barcelona, Sky Sports News understands. The jacket contained his wallet and phone and the Baggies boss was away from the team hotel when the incident took place.