Dundalk FC have admitted that Covid guidelines were breached after pictures emerged over the weekend of a number of first-team players in the North.
The club cancelled training on Tuesday and ordered Covid-19 tests for the players following a team outing to Belfast on Saturday.
Pictures showing several of the Lilywhites squad emerged on Sunday night, with the players subsequently sent home from training on Monday.
While all the results came back negative for the virus, the club acknowledged there was a "serious error of judgement" from those on the trip.
Interim boss and club sporting director Jim Magilton was not believed to have been on the outing but was reportedly llivid when he learned about it.
"Dundalk FC acknowledges that there was a recent breach of COVID-19 protocols and guidelines by some members of the first-team playing squad," a club statement read.
"As a result, all players and coaching staff underwent COVID-19 testing on Tuesday morning. The club can confirm that all tests have since returned negative results. After consultation with HSE Live, the club has determined that no further action needs to be taken."
"Since the advent of the virus, the club has worked in line with the FAI and HSE to ensure a safe environment for all of its players and staff and it is abundantly clear to everyone at Oriel Park that COVID-19 protocols must be strictly adhered to at all times.
"The players fully recognise that this breach was a serious error of judgement and apologise unreservedly for their actions," it concluded.
Bars and restaurants reopened in Northern Ireland last month for outdoor service but people from the Republic have been urged not to travel cross-border for non-essential purposes.