Newcastle's Jonjo Shelvey fractured his hand as he broke up a training-ground fight between captain Jamaal Lascelles and Mo Diame.
The midfielder stepped in and acted as peacemaker when punches were thrown but was caught in the cross-fire.
Shelvey is now wearing a cast but will be fit for next weekend's trip to Southampton.
Lascelles had accused Diame of being 'lazy' before the confrontation on Thursday, which came just 24 hours before it was announced the skipper has signed a new six-year contract.