Lehetséges okok: with regards to copy and paste imports:

• You have not yet imported the player into Hattrick Youthclub or the import was done after you have synchronized the match.
• The player received a red card. If this is the case, then, unfortunately, it is not possible to put him in the line-up because we do not receive the necessary information from Hattrick. This means you need to add the performance of this player and the time he was sent off manually.

Possible reasons: with regards to manual input of players

• You may have entered an incorrect start date for the player's entry into your academy (and this date is later than the date of the match).
• The player's name has been spelt wrong.