Rafa Benitez says Jamaal Lascelles and Mohamed quickly apologised after trading punches in training.
Jonjo Shelvey suffered a broken finger breaking up a fight between the pair at Newcastle United's training ground last week.
Diame, yet to start a Premier League game this season, suggested buying lunch for the team in the wake of the incident.
Manager Benitez said: "To be fair, it was a surprise. It was part of a small training game, and there was a fight.
"Jonjo was in the middle, so he was making peace and everything was fine.
"After the incident, they apologised to each other. Maybe they will buy lunch for everyone. It was Mo’s idea to take the team out to lunch. I don’t know when or how they will do it.
"I have seen worse than that over the years. When you are in the middle of a game, and you are losing or winning, players can react in different ways.
"It is nothing. There's lots worse than that. I told Jamaal that he has to keep pushing in the right way, and Mo is normally training in the right way too.
"Later on they were fine, and they have been training fine without anything special since."
Ninth-placed Newcastle take on Southampton on Sunday.
Shelvey will wear a cast to protect his finger at the St Mary's Stadium.