Guard Kemba Walker sat out Saturday night’s game against the Phoenix Suns with a sore left knee. Walker, who was listed as questionable by the Boston Celtics, didn’t participate in shootaround and underwent an MRI on his knee after telling the team Friday night that he had knee soreness, according to Celtics coach Brad Stevens. “Kemba got ahold of our doctors last night and said he had some knee soreness,” Stevens said. “[He] went and got an MRI today, [and it] didn’t show anything structurally wrong, but he’s very sore.”