Rangers GM Glen Sather said he thinks defenseman Marc Staal will rejoin the team in Europe by the end of this week and questioned whether the headaches that are keeping Staal behind are even related to his February concussion. "There are a lot of things that cause headaches. You can look at migraines -- you can have a slipped disk, you can have pulled muscles, you can have a hundred different things," Sather said after Monday's press conference at Philadelphia's Citizens Bank Park announcing this year's Winter Classic game between the Rangers and Flyers. "Trying to diagnose exactly whether it's a concussion or something else that's bothering a player, that's what you really have to find out first. And, that's been complicated."