Penrod isn't expected to need surgery on his injured left elbow, Chris Cotillo of MassLive.com reports.
Penrod is dealing with a sore left elbow and was sent in for an MRI on Thursday, Gabrielle Starr of the Boston Herald reports.
Penrod was optioned to Triple-A Worcester on Sunday.
The Red Sox selected Penrod's contract from Triple-A Worcester on Saturday, Julian McWilliams of The Boston Globe reports.
Penrod allowed two runs on three hits and struck out seven over 2.2 innings for Triple-A Worcester on Friday.
Penrod (shin) will return from Triple-A Worcester's 7-day injured list to start Friday against Scranton/Wilkes-Barre, Christopher Smith of MassLive.com reports.
Penrod was placed on the 7-day injured list with left shin inflammation Sunday, Christopher Smith of MassLive.com reports.