PITTSBURGH -- The Cubs placed left-hander Mike Montgomery on the 10-day disabled list (retroactive to Tuesday) with left shoulder inflammation and recalled lefty Randy Rosario from Triple-A Iowa on Friday afternoon.
Right-hander Tyler Chatwood will start against the Pirates at PNC Park on Saturday in place of Montgomery.
Montgomery last pitched in a relief appearance against the Nationals last Saturday, when he struck out one and walked one over a hitless inning. He felt something in the game and thought it was just soreness, but he continued to be bothered by the shoulder during his bullpen session Thursday.
"I felt all right the other day, and then I wanted to test it out in the bullpen, and it just kind of didn't feel right," Montgomery said. "It's frustrating, but I think I got to get it right. I've got to get it feeling good. I don't think it's too far off. Just a little discomfort there when I go more game speed."
The 29-year-old is 4-4 with a 3.62 ERA and 1.34 WHIP in 32 games with the Cubs in 2018. Montgomery moved into the rotation in late May, and allowed 27 runs (25 earned) over 73 innings (3.08 ERA) in 13 starts.

Cubs manager Joe Maddon said placing Montgomery on the disabled list was a "precautionary" move to provide more time for the inflammation to subside. Montgomery also indicated he doesn't believe he'll be sidelined for too long.
"I'm pretty optimistic that it's going to be real quick," Montgomery said. "And it will be a good chance for me to kind of get a little breather, kind of build up the strength. Just so I can come back and keep performing at a high level."
Chatwood began the year in the rotation and went 4-5 with a 4.98 ERA in 19 starts. His control proved to be an issue, as he walked 85 while striking out 82 over 94 innings. He's come out of the bullpen for his last three appearances, allowing four earned runs on seven hits with three strikeouts and five walks in 5 2/3 innings. His 90 walks issued leads the Major Leagues.
"Obviously you're excited anytime you get to start," Chatwood said. "Unfortunately, Monty had that, but I'm going to go out there and try to help us win a game. ... I'm excited, I feel good and I'm in a good place."
Rosario, 24, will be available if needed Friday night against the Pirates, Maddon said. The left-hander is 4-0 with seven holds and a 3.00 ERA in 28 appearances with Chicago this season. He struggled his last time out, allowing four earned runs on four hits in one inning against the Padres on Aug. 5.

Darvish on rehab assignment
On Friday afternoon, right-hander Yu Darvish spoke to reporters for the first time since the announcement that he will begin a Minor League rehab assignment on Sunday.
Darvish (right triceps tendinitis) has been sidelined since May 20. He threw about 55 pitches during a three-inning simulated game at Wrigley Field on Tuesday, and told Maddon on Thursday that he felt ready to begin his rehab stint, which will begin with Sunday's start for Class A South Bend.
"I want to come back to the big league level," Darvish said through his interpreter. "And then hopefully be better than my last big league outing. I want to come back stronger than ever."
Darvish has made eight starts with the Cubs, posting a 1-3 record and 4.95 ERA while striking out 49 and walking 21 over 40 innings. He said the main goal of his rehab assignment is to throw pitches without any pain.
"The team's doing really well right now, so hopefully I'll get along with that flow," Darvish said of the impact he can make when he returns. "And then keep the winning streak going."