The team said that he sustained a fracture to his right proximal fibula during first quarter of Saturday's win over the Grizzlies but played the rest of that game. The Mavericks did not give a timetable for his return.
Matthews was a late scratch before Sunday's loss to the Houston Rockets. An MRI on Monday revealed the fracture.
Matthews, 31, has a player option worth $18.6 million for next season. That is the final season of the four-year, $70 million deal he signed with Dallas months after he suffered a ruptured Achilles tendon in his final game for the Portland Trail Blazers.
Matthews, a respected leader in the locker room and valuable mentor for rookie point guard Dennis Smith Jr., averaged 12.7 points and 3.1 rebounds while shooting 38.1 percent from 3-point range this season. He has averaged 13.8 points and 3.2 rebounds with a 3-point percentage of 38.3 in his nine-year NBA career.