TAMPA Defenseman Luke Witkowski arrived Saturday, the latest new face in the evolving Lightning blue line.Don't be surprised if the 24-year-old makes his NHL debut Tuesday against the Canucks."He's definitely going to get a chance," coach Jon Cooper said. "We have to."Why? This is an important evaluation period for the Lightning. It has to see what it has in young defensemen Witkowski, Nikita Nesterov, Andrej Sustr and Mark Barberio before shopping for another defenseman by the March 2 trade deadline.Compounding the issue is that Radko Gudas is out for the regular season following knee surgery, veteran Matt Carle is out indefinitely with an undisclosed injury and Victor Hedman missed two games with a lower-body injury. Odds are theirs won't be the last injuries to pop up."You have to get these guys in at some point, just like Nesterov," Cooper said. "We've got to see what we have because … if things are going to be long term, you've got to get these guys in."Like most teams, the Lightning could use another top-four-caliber defenseman, which would boost a core that includes Hedman, Anton Stralman, Jason Garrison and Carle. It has only two right-handed shots (Stralman and Sustr), which is why Witkowski helps. Carle, a lefty, tried the right side but struggled. Witkowski's size (6 feet 2, 200 pounds) and grit are welcomed, especially with the loss of Gudas. The problem is, every team is looking for defensemen for a playoff push. As general manager Steve Yzerman says, "Top-four (defensemen) are extremely hard to find." Sorry, guys such as Drew Doughty and Shea Weber aren't available. "Teams aren't giving them away," Yzerman said. "Aren't trading them, either."But as teams continue to struggle, you could see defensemen such as Keith Yandle (Coyotes), Jeff Petry (Oilers) and Andrej Sekera (Hurricanes) among the many names that surface. The Lightning has a deep prospect pool and a bevy of draft picks, including two first-rounders this year, to play with. But before Tampa Bay becomes a buyer, it would be helped by figuring out if internal options are at least comparable. Nesterov, 21, has impressed since his New Year's Eve callup. He skates and gaps well and is not afraid of physical play. It was Nesterov's pinch that helped set up Ondrej Palat's winner Thursday against the Oilers. "He's deserved to stay in the lineup, and he's going to continue to do so," Cooper said. "He inched his way in; now he's in."Sustr, 24, in his second full season, is playing with a lot of confidence. Barberio has taken a step despite sporadic duty.Are they enough for a playoff run? The Lightning will find out. Contact Joe Smith at firstname.lastname@example.org . Follow @TBTimes_JSmith.