It was understood that the former Tottenham manager slammed Karsdorp’s attitude immediately after Roma’s 1-1 draw with Sassuolo earlier this month.
Though Mourinho had refused to name Karsdorp at the time but posited: ‘It was a team that wanted to win against a tough opponent, I am sorry that the efforts of the team were betrayed by the attitude of one unprofessional player.
‘An unprofessional attitude that is not fair to his teammates, that is what disappoints me. A point away from home is still not a negative result and I am happy with the general attitude of my squad.’
Mourinho also made it clear that he wants Roma to offload Karsdorp in the January transfer window.
‘I had 16 players on the field tonight and I liked the attitude of 15 of them,’ Mourinho said.
‘I told the other than he had this attitude today only and not always. Now we want to close this period of the season with three points.
‘In January, he needs to find himself another club.’
Karsdorp, who was even berated by his own teammates during the game against Sassuolo, was then dropped for Roma’s final game before the World Cup break.
Roma’s players who are not at the World Cup are due to travel to Japan for a winter training camp but Karsdorp was not at training on Sunday.
National Daily gathered from the reports in Italy that Karsdorp has already left Rome and has travelled back to the Netherlands with his family.
The Dutch defender was signed by Roma in a €19 million (£16.7m) deal in 2017, which made him one of Feyenoord’s most-expensive sales in their history.