I presume because we had a lot of competition to sign him, and generally players come back from clean leg breaks to full fitness without any issues. I'm sure he was given a thorough medical.
I don't think anyone is writing off Knasmuller, it was just terrible timing to take a punt on someone from a league like Austria at mid season with no English experience in a position where we already have Moncur, Mallan, Mahoney and Hammill available, players like that need to come early in summer to get upto speed with language and fitness, and helps if you have at least an idea where they might fit into the team if taking on that gamble
Fair point, we definitely needed players ready to go in January. Fingers crossed he'll come good. With his statistics in the Austrian league, he certainly looked to be worth the punt, regardless of our league position.