Footie bosses have warned Manchester United's Gary Neville and Manchester City's Carlos Tevez about their behaviour after a recent public row.
It comes after Neville made a rude gesture to his former team-mate as City beat United 2-1 in the Carling Cup.
Tevez later called Neville a "moron" for saying the Argentine wasn't worth the £25 million City had paid for him.
The Football Association decided not to punish the players, but is said to have warned them about their future conduct.
Tevez moved from United to City last summer after Alex Ferguson decided not to keep him at Old Trafford.
But before the Carling Cup first leg in Tuesday, Neville said Ferguson was right not to sign the striker.
After his celebrations at scoring both of City's goals, Tevez said: "I don't know what... that moron is talking about me for. I never said anything about him. "
Security has now been increased ahead of the second leg of the tie at Old Trafford, where United will have their work cut out to get to the final.