The words sprain and tear are sometimes used interchangeably.
We've been told that MS has a sprained UCL (ulnar collateral ligament) in his thumb.
A mild sprain involves over-stretching of the ligament.
A moderate sprain involves a PARTIAL tear of the ligament.
A severe sprain involves a complete tear or separation from bone.
If MS had a severe sprain and a COMPLETE tear of the ligament, there's no way he'd even be considered to be ready after the bye.
So IF any tearing was involved, and MS has a chance to play vs. Seattle, it must have been only PARTIAL tearing at most.
Bottom line, people can get sloppy with the word "tear", without indicating the crucial difference between a partial tear and a complete tear.
So yeah, logic and basic medical knowledge and common sense would suggest that MS had either a mild or moderate sprain, given that he missed one week yet has a chance to return 3 weeks later.
And for anyone who gets fussy about it, I'll add the usual disclaimers that I'm just stating my own opinion, and going by general medical knowledge, and yea this is (gasp!) speculation, and I don't have any inside info etc etc etc .