BOSTON -- Despite the many setbacks he has had with his surgically repaired left knee, Dustin Pedroia isn’t giving up.

The second baseman is expected to start another Minor League rehab assignment on Thursday for Double-A Portland, the same day the Red Sox open a seven-game road trip in Chicago.

Pedroia started the season in extended spring training, then played three games on a Minor League rehab assignment for Triple-A Pawtucket.

The 35-year-old veteran was activated for Boston’s home opener against the Blue Jays on April 9. However, his return was short-lived. Pedroia was able to play just six games over a nine-day span. That sixth game was on April 17 at Yankee Stadium, when he felt and heard a pop in his knee and had to exit the game in the second inning.

That setback wasn’t as big as Pedroia and the Red Sox originally feared.

“A lot better [now],” said Red Sox manager Alex Cora. “The way that night [was], it felt like that was it right there. When you talk pop and knee, you don’t feel comfortable with it. I think he feels good. He’s moving well. We’ve been through this the last year. Hopefully we keep getting information, I know there’s new spikes, new brace, there’s a lot of effort into this, so now it’s just go out there and see how it goes.”

After a 2017 season in which Pedroia played 105 games -- most of them with discomfort in his knee -- he had a cartilage replacement procedure done that offseason that no position player has ever had.

Without a precedent to go by, the Red Sox and Pedroia have had to do with unpredictability. His return last season lasted just three games before arthroscopic surgery in July. This time, Pedroia hopes he can find a way to stay on the field. His rehab assignment is likely to be longer than the three-game stint earlier in the season.

“We’ll see how it goes,” said Cora. “He hasn’t played in a while. He needs at-bats. He needs to play. They’ll go over the program and see where we’re at.”

The Red Sox came under some scrutiny for the brief length of the last rehab assignment, and Cora elaborated on that a little on Sunday.

"One thing I don’t know if you guys are aware of, but it’s a little bit different back in the day than when I played,” Cora said. “The player has input on this. I know sometimes it feels like we’re cutting them short or whatever, but it’s just the way it goes nowadays. We do our best to let him know how we feel about it, what we like to do. It’s not that they go over the program or the team but if they feel they’re fine, that’s within the rules. That’s how it works.”

Infielder Eduardo Núñez, who has been out since April 18 with a mid-back strain, will start a rehab assignment for Triple-A Pawtucket on Monday at Buffalo. Brock Holt is already with Pawtucket, as he rehabs from a scratched cornea in his right eye.

There was also news on lefty Brian Johnson, who has been on the injured list with left elbow inflammation since April 6. Johnson threw a bullpen session on Sunday, the first since he suffered his injury. Johnson will throw another one on Wednesday.

J.D. ‘better’, but out again

The Red Sox again posted a lineup without star slugger J.D. Martinez for Sunday’s 5-2 loss against the Rays. The DH was out a second straight day with back spasms. Cora didn’t rule out that Martinez could pinch hit before the game, but Martinez did not make an appearance in the loss.

“J.D is better, but not better, you know?” Cora said pregame. “Still tight. I think we’ll try to stay away from him today. If needed, we’ll use him later on depending on how he progresses during the day. Not starting him is the smarter thing to do.”