The pair are reported to have squared up to each other during a training session after the skipper branded Diame "lazy".
Jonjo Shelvey is then said to have physically inserted himself between the players in order to prevent tensions from escalating and wound up with a broken finger for his troubles.
Facing the media for the first time since the spat today, Benitez played down the row and claimed that he had seen "much worse" in the past.
"It was a surprise, it was part of a small football competition. [There was] a fight, everybody knows there was a fight," he said. "Jonjo was in the middle, he was making peace, and everything was fine.
"After the incident they apologised to each other and they will maybe pay for lunch for everyone. That was Mo's idea.
"I've seen worse than that, so many players, so many years. It was a normal thing that sometimes happens when you are challenging for something or in the middle of a game. It was nothing."
Shelvey is expected to play with a cast when the Magpies travel to Southampton on Sunday afternoon.