He had a torn MCL (IIRC) that looked way worse initially than it ended up being, so it only required a minor surgery and he could return to training 4 weeks later. Says it works just like before.
As for the match-up itself, I wouldn't underestimate Teemu's dynamic finishing skills and killer instinct against a fighter like Held who, although certainly is the better and more technical grappler, can tend to be a bit passive in his offensive output. If he gives Teemu too much space and allows him to get some 50/50 exchanges off, he could end up getting his bell rang one way or the other.
Teemu has a sizable reach and height advantage in this fight and his uppercut is arguably his strongest weapon on the feet, which works wonders against a grappling based, shorter fighter like Held who has to find a way inside. Packalen packs quite a lot of power for a lanky-looking hipster, so all in all, his threats on the feet shouldn't be overlooked, no matter the fact that he got blasted by Diakiese the way he did.
Also, a pretty funky statistic about Packalen that is worth mentioning is that whenever he took a guy down in his pre-UFC career, he finished the fight before either the guy could escape or the round ended. His elbows from the top are damn punishing.
If I didn't manage to sell him to you yet, here's Packalen vs Gouti for good measure:
Ps. I'm biased.