Summary
Last summer, Muscala had a player option for the minimum. Now, there isn't a whole lot of reasons to pick up an option for the minimum, since declining the option means you get more options and essentially the same money even if you settle for the minimum as a free agent. The primary reason not to pick up a minimum option is if you're unsure you'll even get a fully-guaranteed minimum contract as a free agent. Needless to say, Muscala picked up his option.
 
While he has consistently shot well from outside, he isn't an elite outside shooter, and doesn't do anything else. Stretch bigs can be valuable, and Muscala had some nice moments for the Thunder this season, but it's hard to imagine many teams being super interested in signing him. I'm not saying Muscala doesn't belong in the NBA, but I also wouldn't be surprised if he wasn't on a roster next season either.
 
Cap Considerations
Muscala will be an unrestricted free agent with a $1.7 million cap hold and Early Bird rights. The Thunder could offer Muscala a starting salary of up to 5% more than the average salary (likely around $10 million) using the Early Bird exception, which will be more than enough should they wish to bring him back.
 
Other teams will have multiple ways to sign Muscala as even teams without cap space could possibly use any of the Non-Taxpayer MLE, Taxpayer MLE, or possibly even the Room MLE or Bi-Annual Exception to sign him. It's likely that Muscala would only get minimum offers this summer.