Schalke forward Rabbi Matondo has apologised after a photo posted online showed him wearing a Borussia Dortmund shirt, emblazoned with Jadon Sancho's name and number, while taking part in a gym workout.
Dortmund and Schalke are arch-rivals in Germany's Bundesliga, and fans of the Gelsenkirchen club were unhappy to see one of their players wearing the kit of one of Borussia's star players.
Matondo apologised on Instagram, with the 19-year-old Wales international stating that he had not wanted to cause anyone "grief or trouble".
He wrote: "I am very sad and disappointed in myself that I have let down anyone who feels connected to Schalke. I was naive and put the jersey on for a private training session. The jersey was from my close friend Jadon Sancho. I only wore it because of Jadon, it had nothing to do with Dortmund.
"I did not think about the consequences and that it would annoy many people. There is no excuse for this immature behaviour. I can promise every Schalke player that I have identified with Schalke 100 percent since day one."
The picture was posted online by a gym in Cardiff where Matondo was training although it was later deleted following the angry reaction online from Schalke fans.
Matondo has been a prominent first-team player for Schalke ever since he moved to Germany from Manchester City in January 2019 in an £8 million deal, following the path trodden by his friend Sancho from the Premier League club’s academy to the Bundesliga in search of more first-team opportunities.
In 2019-20 he featured 20 times for Schalke in the Bundesliga, scoring twice, as David Wagner’s side endured a poor season which saw them finish 12th, just eight points above the relegation play-off place.
They failed to win a single league match after January 17, putting in a series of poor performances in the second half of the season, particularly after Bundesliga resumed following the hiatus in the campaign enforced by the coronavirus pandemic.
The nadir came when they were thrashed 4-0 by rivals Dortmund, which has served to deepen the resentment of Schalke fans and cause an even stronger reaction to Matondo’s error of judgement.