Tottenham have criticised three of their players for attending a party over the Christmas period.
A picture circulating on social media shows Erik Lamela, Sergio Reguilon and Giovani Lo Celso together at a party along with West Ham's Manuel Lanzini.
A spokesperson for Tottenham said: "We are extremely disappointed and strongly condemn this image showing some of our players with family and friends together at Christmas particularly as we know the sacrifices everybody around the country made to stay safe over the festive period.
"The rules are clear, there are no exceptions, and we regularly remind all our players and staff about the latest protocols and their responsibilities to adhere and set an example. The matter will be dealt with internally."
Spurs boss Jose Mourinho also expressed disappointment at the players' actions after Saturday's Premier League win over Leeds.
He had been critical of the Premier League for cancelling his team's match against Fulham in midweek after a virus outbreak in the Cottagers' squad.
But his players' antics put him in an awkward position and he gave them a stinging blast, even referencing the present of a suckling pig he gave to Spanish defender Reguilon for Christmas Day.
"I gave an amazing gift, Portuguese piglet. Amazing for Portuguese and Spanish. I was told he (Reguilon) would spend Christmas on his own. He was not alone as you could see," he said.
"We feel disappointed because we gave the players all the education and conditions. We are not happy. It was a negative surprise for us.
"We know what we are internally. We don't need to open the door to you and let you know what is going on internally.
"What are going to be the consequences and how deeply we approach that negative surprise...I feel disappointed."
Lamela was not included in the matchday squad for Saturday's Premier League fixture against Leeds, with Reguilon relegated to the bench. Lo Celso is unavailable through injury.
This is not the first time Spurs' players have broken UK lockdown rules as there were several incidents during the first lockdown in the spring.
Mourinho was seen holding a personal training session with Tanguy Ndombele, Ryan Sessegnon and Davinson Sanchez were seen out running together, while Serge Aurier had a haircut and a personal training session with Moussa Sissoko.
West Ham also reminded Lanzini, who scored a last-gasp equaliser against Spurs in October, of his responsibilities.
A West Ham United spokesperson said: "The club has set the highest possible standards with its protocols and measures relating to Covid-19 so we are disappointed to learn of Manuel Lanzini's actions.
"The matter has been dealt with internally and Manuel has been strongly reminded of his responsibilities."