The League One club launched an inquiry after images appeared on social media of posts in a private chat following England’s Euro 2020 final defeat by Italy earlier this month.
The whole squad was suspended while the investigation was ongoing, but those who were found not to be involved have now been allowed to return to training.
A statement issued on the club’s official website said: “Portsmouth Football Club have concluded an investigation into discriminatory messages that originated from an Academy U18 private group chat.
“A disciplinary process will now begin, which – in line with club policy and employment law – will last for a minimum of five working days.
“All members of the U18 side were suspended while the investigation took place, but those who are not involved in the disciplinary process have now returned to training.
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“With that in mind and in regards to this sensitive matter, Portsmouth FC would continue to respectfully appeal for everyone’s consideration in their use of social media posts directed towards any of its employees and, indeed, any other external parties.