The bullpen session was Uehara's first since he sustained the injury a couple of weeks ago. The hope was that Uehara would be able to pitch in a Grapefruit League game on Monday, and pitch three times during the final week of Spring Training.
Now, the best-case scenario is that Uehara can throw a bullpen session without soreness on Monday, followed by game appearances on Wednesday and Friday.
"Not going to go that far yet," said Farrell, when asked if the clock was working against Uehara for Opening Day.
"Realizing that we're 10 days or nine days from opening, even if Koji were to get in a couple of games, I think, we'd still remain open-minded to beginning [with him]. We're talking about a one-inning reliever, a veteran guy, who has been able to keep his arm in shape, at least through long toss and at least some flatground. This is still day to day at this point."
Uehara has pitched in three Grapefruit League games, the last on March 14.
• Right-hander Joe Kelly responded well to Friday's Minor League start, his first game activity of any kind since suffering a biceps injury on March 16.
Kelly will pitch Wednesday, either in a Grapefruit League game or the Minors. It remains unclear if Kelly will start the season on the Opening Day roster.
With an off-day on April 7, the Red Sox could bring back Clay Buchholz on four days rest for the fifth game of the season and activate Kelly the next day.
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.