Great Britain were disqualified from the men's 4x400m relay at the European Athletics Team Championships after a reserve shot putter was named in the line-up by mistake.
Youcef Zatat, who did not travel to Poland, was included in the quartet instead of sprinter Rabah Yousif.
UK Athletics performance director Neil Black blamed a "technical error".
He told BBC Sport: "It's absolutely gutting, for the athletes in particular."
Youcef Zatat tweeted that he "definitely" would have run in the relay.
As a result of the increased attention, he joked that he was now taking "bookings for club appearances and other public events".
He added: "As funny as this has been for me I feel for the guys who went all that way to not run."
Britain finished fifth overall with 302.5 points. Italy won the 4x400m race and finished fourth in the overall standings with 316 points.
Twelve points were available for each event's winner, with 11 available for second place - meaning GB would still have finished fifth if they had won the 4x400m and Italy had come second.
Black added: "There was a technical error with the declaration process. We're exploring what happened.
"The athletes were absolutely amazing. We informed the athletes and they took it on the chin."
Britain's men won the silver medal in the 4x400m relay at the 2018 European Athletics Championships, and took bronze at the World Athletics Championships in 2017.
They were also disqualified at the 2016 Olympics in Rio.