High ankle sprain.
There was a huge dropoff in performance when Alt's replacement came in at LT.
Still, it's better news than what I was expecting, seeing how he was carted off the field.
Link: https://www.nbcsports.com/nfl/profootballtalk/rumor-mill/news/report-joe-alt-is-expected-to-miss-multiple-weeks-with-high-ankle-sprain