Manchester United manager Jose Mourinho is unhappy with Everton counterpart Ronald Koeman for publicly expressing an interest in Memphis Depay.
Expectations were high after one of Europe's most sought-after players made a big-money move from PSV Eindhoven last summer.
However, Depay has flattered to deceive at Old Trafford and September's EFL Cup tie at Northampton represents his only competitive start under Mourinho.
An exit for the Holland international, who scored twice against Luxembourg, looks increasingly likely, with compatriot Koeman confirming his interest "if there is any possibility'' of signing the winger.
The Everton manager attempted to buy him when at the Southampton helm and public talk of a January move has irked United boss Mourinho.
"I prefer not to make [a response to Koeman's comments],'' Mourinho said. "I prefer not to make.
"I think that my normal answer if somebody asks me about a player from another team, my normal [answer] is 'the player is not my player, the player belongs to another team, the player belongs to another manager, no comments at all'.
"I think that is the ethical [answer] and when we are always worried about ethics and respect, and rules, I just said that if it was me making that kind of comment about an Everton player, I would be in trouble.''