The 24-year-old is currently seeking a second opinion from a specialist, Haynes adds.
It's unclear exactly when Oubre suffered the injury. However, he was held out of the Suns' loss to the Los Angeles Clippers on Wednesday due to a knee concern.
Head coach Monty Williams said before Wednesday's contest that information surrounding Oubre's injury was still scarce.
"I don't want to speculate because the information is still fluid," Williams said at the time, according to Duane Rankin of AZ Central. "So we'll see. I'll find out more. We just found out yesterday so I'm still trying to figure out when it happened and what contributed to it."
Oubre is averaging career highs in points (18.7), rebounds (6.4), and assists (1.5) per game this season. He's also shooting a personal-best 35.2% from deep on 5.5 attempts per game.