If there is one thing that the Ottawa Senators cannot afford, it’s to lose superstar defender Erik Karlsson for an extended period of time. In part, that’s why Karlsson had off-season surgery to repair torn foot tendons – to ensure that long-term, the nagging pain goes away. But there are two sides to every coin, and on the other side is the reality that the recovery from such a surgery appears to be a long one. Karlsson, right now, has a two-to-three week timetable before he begins skating with Ottawa. And whether he returns towards the end of October or at some point in November, it’s clear he’s going to miss some regular-season games. That, of course, is unfortunate news for Ottawa. The Senators were one of the biggest surprises of last season – a team that was better than most stats-savvy people expected, but one that still had a number of positional holes. No area in Ottawa is more vulnerable to depth issues than the defence, and, knowing that Karlsson could miss anywhere from five to 17 games to open the year, it’s an immediate concern for head coach Guy Boucher. The depth issues behind Karlsson have basically been a problem his entire career in Ottawa. Karlsson joined the NHL in 2009-10, and by 2010-11 had become one of the league’s premier defenders. But outside of last year’s run to the Eastern Conference Final, Ottawa hasn’t had a ton of success during that stretch. That’s at least in part due to the fact that the Senators have been a historically average – and in many years, that’s being kind – team when Karlsson’s off the ice. Even though Karlsson can perhaps play more minutes than any other player in the league, there’s still an awful lot of time where he’s watching from the bench as his team is mercilessly shelled.