Forward Eric Nystrom skated this morning at Joe Louis Arena, but was ruled out by the Predators with an “upper body” injury for tonight’s game at Detroit. Nystrom took a punch behind his ear last week against the New York Islanders. “When you get knocked there, it affects your balance a little bit,” coach Barry Trotz said. “He’s fine. He’s a tough kid, it won’t affect him.” Mazanec first goalie off ice: Trotz would not divulge his starter for Tuesday’s game, but rookie Marek Mazanec with the first goaltender off the ice at morning skate. This would mean Mazanec will likely get his third straight start.