Next in Uehara's progression will be a bullpen session on Wednesday, then another batting practice session in Oakland on Saturday.
"I wouldn't rule out activation after the BP," said Farrell. "Again, I think in fairness to Koji, what we've done is just review how he feels after each work session and we'll take it from there."
Uehara would probably get a day of rest on Sunday, and his activation could come the next day, when the Red Sox open a three-game series in San Diego.
"It doesn't really matter what time of the season it is. Whether it's April or September, I'm always willing to contribute to the team," Uehara said.
The Minor League seasons end on Sept. 5, so a rehab assignment isn't an option. The return of Uehara could be important for a team that has had a lot of trouble in the eighth inning the past few weeks.
"It makes no sense to rush at this point in time, so I'll try to be ready when I'm ready," said Uehara. "I think the biggest hurdle is getting over the hurdle mentally. I think I'm pretty good where I am physically."
"The one thing Koji's proven to us is even with some very limited Spring Training work, he's been an effective pitcher for us," said Farrell. "And honestly, he has a chance to make a very positive impact once he does return and we'll know that date as we get further along here."
When Uehara strained his right pectoral muscle on July 20, there were no guarantees that he would pitch again this season. But he's turned a corner in recent weeks.
"To his credit, he's worked his tail off and he's gone about this in advance fairly rapidly based on the way he feels and he's withstanding the intensity that he's putting into it," said Farrell. "Today was an aggressive bullpen [session]. It wasn't one to just kind of work through your delivery. He was getting after it in good fashion."
• Backup catcher Ryan Hanigan, who has been on the disabled list since Aug. 6 with left ankle tendinitis, will be activated by the Red Sox on Friday in Oakland. He is in the midst of completing a Minor League rehab assignment with Class A Short Season Lowell. The Red Sox could eventually have four catchers in September, as Christian Vazquez could be promoted once the Triple-A season ends. Sandy Leon and Bryan Holaday are currently sharing the catching duties.
• The Red Sox helped to kick off the annual Jimmy Fund radio-telethon with WEEI and NESN on Monday, with several players stopping by to support a good cause. Farrell, who had cancer last year, is proud of how supportive his players are to helping the Jimmy Fund raise money to help prevent the disease.
"It says a tremendous amount about their understanding of their place in our city and our region," Farrell said. "The more that we can be a presence, and hopefully make an impact, the better."