Armstrong was recalled from Triple-A Columbus on Friday.
The Tribe went ahead and swapped out Kyle Crockett, who pitched each of the last two days, for a fresh arm in Armstrong. It will be Armstrong's third stint with the big league club this season. He has been able to overcome some control issues at Columbus, posting a 1.96 ERA despite a 5.5 BB/9 rate, but Armstrong will have a tough time earning high-leverage work in Cleveland's strong bullpen.