During Saturday night's game between the Lightning and the Chicago Blackhawks, Stamkos took an awkward fall during a battle for the puck. Nothing appeared to be wrong until he tried to stand up. He stumbled, grabbed at his knee and eventually hobbled off the ice. Stamkos left the game and did not return. Many suspect a ligament tear or similar injury.
For Stamkos it's another in a long list of injuries during his career. It's a shame he's missed to much time because he truly is a special talent in the NHL. Unfortunately, hockey can be a cruel game and the reality is, the Lightning without Stamkos are still a very good hockey team. While his absence in the playoffs would definitely be felt, the Leafs will still need to bring an effort above and beyond the norm to get past the Bolts.
I'd imagine we'll have an update on Stamkos at some point tomorrow or Monday.