Cleveland Indians ace Corey Kluber has what is being termed a "mild strain" of his quadriceps muscle. In the same Tweet, Indians beat writer Jordan Bastian says the expected timetable for his return to the mound is 7-10 days. That means Kluber's regular season is over (as are his chances of winning the Cy Young this season), but he should be able to rejoin the rotation for the ALDS, likely to pit the Tribe against the Rangers or Red Sox.
Game 1 of the ALDS will be next Thursday, October 6, which is nine days from now, so it's entirely possible Kluber will be on the mound for that one, but is also possible he's not quite ready.