Brandon Workman could be another pitcher who resurfaces in the coming days or weeks.
Webster went 1-2 with an 8.60 ERA in eight games for the Red Sox last year, seven of which were starts.
He hasn't been up to the Major Leagues yet this season, but has been effective for Pawtucket, going 4-4 with a 3.10 ERA in 21 starts.
"He has been able to maintain the overall command of stuff more than a year ago," said Farrell. "And he's gotten another 20-plus starts under his belt at the Triple-A level, which when you take back last year, his year at Triple-A was a very good one for us. He's in the process of transitioning to our level here."
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.