The 37-year-old left-hander held a showcase for teams around the middle of July and is still in the process of getting stretched out in Arizona.
Hamels, a staple of dominant Philadelphia Phillies teams, has a career 163-122 record with a 3.43 ERA in 2,698 regular-season innings.
In another move on Wednesday, right-hander Jimmy Nelson was placed on the injured list because of right elbow inflammation.