CHICAGO -- The Red Sox walking wounded are getting a little closer to returning.

Second baseman Dustin Pedroia (left knee discomfort) started his rehab assignment with Double-A Portland on Thursday, batting second and playing second base. He played five innings and was 0-for-3 at the plate.

Pedroia has played just six games with the Red Sox this season after returning from the injured list on April 9.

“There’s a plan in place, and just like I said, he’s going to push himself to be an everyday player. That’s something that we want, too,” manager Alex Cora said Thursday. “We talked about our situation, where we are at roster-wise and all that, and he agreed to it. He understands. For him, too, it’s good. That’s who he is.”

Eduardo Núñez (mid-back strain), who began his rehab assignment with Triple-A Pawtucket on Monday, is starting to take more reps in the infield. The utility man has been the designated hitter in two of his three rehab starts, but he did play third base on Tuesday.

“Nuney’s going to play tomorrow, again,” Cora said. “He played today, he DH’d. It was wet. That’s why he didn’t play second or third. Tomorrow he’s going to play second base. He’s getting close.”

Infielder Brock Holt did not travel with the team to Chicago, staying in Boston to receive treatment on his right shoulder impingement. Holt began a rehab assignment after a scratched cornea on Friday, but was shut down after experiencing shoulder discomfort Sunday.

He has not begun baseball activities, according to Cora.

Left-hander Brian Johnson did make the trip with the team and has ramped up his baseball activities. Johnson was placed on the 10-day injured list with left elbow inflammation on April 6.

“He threw a 'pen yesterday. He felt good. He threw breaking balls,” Cora said. “Maybe one more. Maybe a simulated game, but he’s getting better.”