UFC welterweight champion Georges St-Pierre has injured his knee for the second time in two months, forcing him out of action once again. But this injury is much worse than the one that cost him a few weeks and a date with Carlos Condit in October.This time, the champ tore his ACL and will be out around 10 months, UFC president Dana White announced.The issue will cost him a spot in the UFC 143 main event, and one of 2012's most anticipated matchups against former Strikeforce champion Nick Diaz Instead, Diaz (26-7, 1 no contest) will face Condit in a bout that White says will be for the interim welterweight championship.As you may recall, Condit (27-5) has had a roller coaster ride in the booking department recently. After knocking out Dong Hyun Kim at UFC 132 , he was going to fight BJ Penn at UFC 139 , then got the slot against St-Pierre when Diaz went AWOL for two press appearances. But that opportunity came and went when St-Pierre suffered his first knee injury.Condit didn't end up fighting in October, instead choosing to wait for St-Pierre to heal. But even that plan went awry when Diaz overwhelmed Penn, and St-Pierre insisted upon fighting the Stockton, California native.So Condit was moved aside and thrust into a matchup with Josh Koscheck . And now Koscheck is the odd man out.That's enough to make your head spin, but the long and short of it is that the Condit-Diaz winner will be the interim champ, and whenever St-Pierre returns, he'll face the holder of that faux belt.This is the second major injury St-Pierre (22-2) has suffered as champion. During a successful July 2009 title defense against Thiago Alves , he tore his groin and didn't fight again until over eight months later.By the time he returns, St-Pierre will have had over a year on the sidelines. His last bout was an April 2011 unanimous decision win over Jake Shields. He has been the champion for over 1,300 days, since wresting the title from Matt Serra in April 2008.