That's even worse than it actually sounded.
First, it was a sore knee. Now it's a sprained MCL.
Paul Pierce may look like slow on court, but he has a very quick first step, which is one of his lethal assets. And from what I've seen in game 5, he was struggling with his lateral movement.
So, we can't expect him to magically be 100%, I suppose, but I hope it feels better in time.