I'm guessing he wasn't 100%.
via Rotowire:
Trail Blazers' Anfernee Simons: Leaves early Friday
Simons has been ruled out for the rest of Friday's game against the Clippers due to a left knee injury. He recorded three points (1-6 FG, 1-4 3Pt), six assists and one steal in 22 minutes before leaving.
Simons had been listed as probable heading into Friday's game while battling tendinitis in his left knee, so he may have aggravated the injury at some point during the contest. The team will likely re-evaluate Simons early Saturday, but it wouldn't be surprising if he ended up being held out against the Nuggets in the second leg of a back-to-back set