Frank Lampard appeared to tell Roy Keane to 'get some f****** balls' during a touchline exchange in Monday night's East Midlands derby.
In a clip circulated widely on social media, Derby manager Lampard stormed up to Nottingham Forest assistant manager Keane in the 75th minute.
And fans on Twitter reckon they know what the Chelsea legend told the former Manchester United hardman.
Lampard's eyes were locked on Keane as he marched down the touchline and appears to say 'get some f****** balls' at the Forest assistant, who is watching the action on the pitch.
The pair were rivals on the field when Chelsea and United went head-to-head in the Premier League during the early noughties.
But it was Keane who gained the upper hand on Monday night as Forest beat Derby 1-0 thanks to Yohan Benalouane's second-minute goal to boost their Championship play-off aspirations.
Martin O'Neill's Forest are now just a point behind the Rams and within three of the play-offs following their win in a typically heated local derby.
Fans waded in on Twitter, with Chelsea fan Will Reyner writing: 'Lampard actually told Roy Keane to get some f*cking balls. That takes balls from Frankie.'
Another user, Jack, replied: 'However good tonight was I'm heavily disappointed that Roy Keane didn't head butt Lampard.'
Kai referenced the Leeds United manager Marcelo Bielsa and the Spygate affair which involved Derby, saying: 'Lampard telling Keane to grow some balls that's rich coming from the bloke who was about crying cos someone was watching his training sessions.'
Keane, 47, had previously worked as O'Neill's right-hand man with the Republic of Ireland national team and they were reunited at the City Ground at the end of last month.
Their aim is to lift Forest into the play-off spots and that moved significantly closer with Monday night's victory.
Lampard, who took over as Derby coach last summer, his first managerial role, has them positioned on the edge of the top six.