The French winger, who moved to White Hart Lane in the summer of 2016, has been pictured donning the colours of Spurs’ London rivals.
He has faced a backlash on social media, with some fans calling for his contract to be ripped up.
NKoudou, though, insists that he is an innocent party and never meant to cause any harm.
He says the training jersey was merely a gift from former Marseille team-mate Michy Batshuayi – a man who helped Chelsea to the Premier League title last season.
Lol @ clickbait ... I'm wearing the shirt my friend @mbatshuayi gave me... NO disrespect here just old friendship sorry for not knowing— GK NKoudou (@gknkoudou) June 20, 2017
NKoudou, who joined Spurs in an £11 million deal, was restricted to just 14 appearances in the 2016-17 campaign.
Only six of those outings came in the Premier League, as other members of Mauricio Pochettino’s squad pushed the club into title contention.
They were ultimately unable to chase down Chelsea, with Batshuayi netting the goal which eventually confirmed the Blues as champions.
NKoudou will be looking to play a more prominent role next season, allowing him to win back any favour he has lost in the eyes of certain Tottenham followers.