McTaggart pointed out yesterday that the 2017 AL MVP played through knee pain throughout the second half of this season. Still, the exact diagnosis has not yet been revealed by either Altuve or the team, and the Astros have yet to confirm the surgery. As of right now, Altuve is expected to make a full recovery in time for Spring Training.
Altuve was the DH for the final three games of the ALCS against Boston, but manager AJ Hinch said the injury would have sent Altuve to the disabled list had it been the regular season. Presumably, the knee worsened as the year wore on. Altuve originally injured the knee while sliding into second base in a game against Colorado all the way back in July.
Before the injury, Altuve hit .329/.392/.464, whereas after the injury he hit .276/.366/.409. Nevertheless, the three-time AL batting champ still finished the season with an overall slash line of .315/.384/.449 and 134 wRC+.