Hammel, who hasn't pitched since July 13 after undergoing right knee surgery, will fly to Baltimore on his own Wednesday afternoon before the Orioles finish their three-game set in Toronto.
"He's physically fine, it's not a medical thing anymore," Orioles manager Buck Showalter said. "They signed off on that. He's physically ready to go."
Hammel's pitch count will be limited, but Showalter wouldn't specify any exact details.
The right-hander is 8-6 with a 3.54 ERA over 109 1/3 innings this season. Showalter believes his small workload will benefit the club down the stretch run, as it battles for the division title.
"It's like making a pretty good September trade," Showalter said.
With Hammel starting Thursday, Wei-Yin Chen will get an extra day of rest and start Friday.