The former England star took to social media to share his disappointment in the incident that marred Derby County's 1-0 Championship win at The Den
Derby coach Wayne Rooney has condemned the behaviour of Millwall fans as "disgraceful and mindless" after they jeered players for showing support to the Black Lives Matter movement before kick-off on Saturday.
The Millwall and Derby players knelt before the start of the game in a gesture of support for the campaign against police brutality towards black people.
Millwall criticised the supporters' behaviour and pledged to prevent a repeat of the incident in subsequent home matches.
Interim Derby manager Rooney expressed his "surprise" in an interview after the game, but has followed up with a stronger message denouncing of those responsible.
"Yesterday I witnessed the disgraceful and mindless behaviour by a large section of the Millwall supporters in the stadium," Rooney wrote in a social media post. "Prior to the match, we were aware of the possibility of a planned disruptive response during the taking of the knee in support of the BLM campaign, but nothing prepared us for what we heard.
"I was proud of my players and staff for not letting the fans deter them from continuing to present a positive and important message that taking the knee immediately before a game sends. The professionalism of the players on both sides throughout the game was a credit to our profession after such an incident.
"On behalf of Derby County, I want it to be clear to everyone associated with the club that we represent all sectors of our community, regardless of colour, gender or sexuality.
"Fans being allowed back into the stadiums is vital for the wellbeing of everybody involved in our sport, from fans to players to chairmen and owners. It is therefore really important that the vast makority of us show respect and support of each other and do not tolerate or accept the actions of the mindless few."
Millwall manager Gary Rowett told reporters that his players fear taking the knee is in danger of becoming an empty gesture and urged clubs to do more off the field to fight discrimination.
“The players have released a statement together and said they don’t support it [taking the knee] as a political message but support anti-discrimination," he said. “Moving forward, like a lot of clubs, they would prefer not to take the knee and actually enact change.
“They want to be proactive rather than it being a gesture, which a lot of clubs are now saying is perhaps empty. That’s not my consideration, but they now feel that gesture is in danger of being empty.”