Tottenham midfielder Eric Dier climbed over seats in a stand to confront a fan who "insulted" him after Spurs were knocked out of the FA Cup at home by Norwich, says manager Jose Mourinho.
Dier, whose brother was in the stand and "not happy" with the situation, was eventually held back by stewards.
Mourinho said: "I think Eric did what we professionals cannot do but probably every one of us would do."
The Football Association and Tottenham are investigating the incident.
Dier, who has 40 England caps, scored in the penalty shootout defeat by Norwich, but keeper Tim Krul saved two efforts to put the Canaries into the quarter-finals of the FA Cup.
Mourinho said: "I repeat we professionals cannot do it, but I repeat I am with the player and I understand the player. The fans were with the team until the last penalty kick that we missed.
"This person insulted Eric, the family was there, the younger brother was not happy with the situation."
On the prospect of the club taking action against Dier, Mourinho said: "If the club does that I will not agree, but he did wrong."
The incident happened in the area behind the dugouts, which is a corporate section, and Mourinho criticised it for not housing "real Tottenham fans".
He added: "The people that are in these privileged positions by the tunnel, of course some are Tottenham fans.
"But I think a lot of corporate, a lot of invitation, a lot of people with special status [are in there] and probably it is the place of the stadium where I sometimes have doubts over if they are the real Tottenham fans, because these [real fans] are the ones who support the boys until the last."
Video on social media shows Dier running and jumping over the pitchside barriers into the stand at the end of the game. He makes a beeline for a fan and clambers over seats until he reaches the top row of seats in front of the hospitality boxes.
Another video shows him being restrained by fans and security, while shouting "he's my brother". He is then led away by security with his arm around a fan.