He came out of the game after surrendering a solo home run to Rays catcher J.P. Arencibia in the seventh inning, after which catcher Alex Avila visited him on the mound and immediately motioned for manager Brad Ausmus and head athletic trainer Kevin Rand to assist.
According to Ausmus, the tightness has been an issue Farmer has dealt with lately and, as such, the team has recently been trying to avoid using him. Farmer last pitched on September 2 against the Kansas City Royals.
Farmer said he felt some discomfort on the Arencibia pitch. He said the cooler weather might have been a factor in it tightening as well.
"Getting warm, going out here and sweating and then coming in and sitting down letting me get cold may have had something to do with it," Farmer said.
Farmer said he was frustrated with the setback but doubted it would prematurely end his season.
"Just take it in stride," Farmer said. "It's not going to shut me down I don't think. I'll be back."