Their personalities have rubbed against each other for a while now. It played out behind the dressing-room door, away from the cameras.
Outlook
Repeated incidents may damage dressing-room status.
Wants European football
Serious
Cause
He is at an age where he expects Champions League / Europa football, and the club cannot offer it. (He is openly ambitious.; The club has no realistic path to continental football.)
Outlook
Contract request risk increased.
Reassured by the manager's half-time message
Minor
Cause
The team were behind, and the manager needed a response. His professionalism usually steers him back from these moments.
Outlook
Trend is improving — relationship should keep strengthening.