Carmelo Anthony stood in the dark tunnels of the arena in Cleveland on Monday night, smiling assuredly and insisting he had no worries about his right knee. An MRI taken last week had provided some consolation for Anthony as he worried over the last few weeks about the pain in the back of his knee. And an examination Tuesday after he arrived in Detroit reinforced the notion that there was no structural damage. The Knick forward’s diagnosis is a stiff/sore knee, and he is listed as questionable for tonight’s game against the Pistons. But left unanswered is the question of just what has caused the problem. Anthony fell to the floor in the second quarter Monday, with his night ending after just 14 minutes, 15 seconds. Anthony left the game after tumbling to the floor in the open court at Cleveland, but said later that the injury did not occur on that play — and that he had been bothered by pain in his knee for weeks and woke up with it feeling worse Monday. “One day I took an MRI on it, just to get some clarity,” Anthony said Monday night. “The MRI [last week] came back great, wasn’t really nothing. So there’s really nothing that we can figure out at this moment. “[Monday] I just woke up — some days you wake up and you don’t really feel right. I came and I tried to warm up in warm-ups, and it still didn’t feel right. I thought it was going to loosen up before the game. Some of the things that I was doing, it felt like I was dragging my leg, and then that one particular play as well.” Anthony has missed seven games this season: two with a hyperextended left knee, two with a sore ankle, two with a lacerated finger and one while serving a suspension. The Knicks are 3-4 without him. If he can’t go tonight, the Knicks are left to figure out how to make up for his scoring output. Amar’e Stoudemire stepped into the breach Monday, scoring 22 points and topping the 30-minute limit imposed by the team’s medical staff (playing 31:55).