UEFA has issued a warning to the Irish Football Association after Northern Ireland players wore branded clothing during open training.
During the session on Tuesday, a designated UEFA open day, players were expected to avoid any sponsor branding.
However, they began the workout wearing standard training shirts before covering them up with UEFA bibs.
A UEFA spokesperson told Sky Sports News HQ: "We were informed that due to a logistical issue, the Northern Ireland team did not have their unbranded training kit available for this open training session.
"We were satisfied with their explanation but they will be warned to avoid a repeat of this situation and we don't expect it to happen again."
The Irish FA is experiencing a European Championship finals for the first time at what is their first major tournament since the World Cup finals of 1986.