CHICAGO -- Before the All-Star break, the Cubs had Adam Warren make a spot start to give the other five pitchers in the rotation a breather. They will do it again on Sunday.
Kyle Hendricks was scheduled to start Sunday, but he will be replaced by lefty Brian Matusz, 29, who has been pitching in the Cubs' Minor League system since he signed with the team on June 14. Matusz was traded by the Orioles on June 1 after giving up eight earned runs over six innings in seven games, then released by the Braves.
In two starts at Triple-A Iowa, Matsuz gave up two earned runs over 9 1/3 innings for a 1.93 ERA, striking out 11 and walking three. He was scheduled to start Friday, but he was scratched from that game against New Orleans.
"He can pitch," Cubs pitcher Jake Arrieta said of Matusz, who was his teammate on the Orioles. "He's a smart guy. He's got some really good pitches he knows how to use effectively. I look forward to watching him pitch and catching up with him."
Prior to Chicago's 4-1 loss to Seattle on Saturday, Cubs manager Joe Maddon said the rotation was "subject to change" and the announcement was made after the contest. Right-hander Justin Grimm was optioned to Iowa to make room for Matusz.
"As we've talked about all along, we're attempting to give our regular five a rest at particular moments, so we're considering doing something right now," Maddon said.
It's not that the Cubs' starters are struggling. The rotation boasts the best ERA in the Majors at 3.02. Since the All-Star break, the pitching staff has a collective 2.48 ERA.

"We just think it's prudent to be proactive," Maddon said. "I do believe you will see more of a trend in the future, where teams interject a sixth guy pre- and post-[All-Star break]. I'm seeing now that if you have a guy you really like, it's important pre-All-Star break to interject someone. When you get the opportunities, take advantage of it."
• Anthony Rizzo did not start Saturday, a rare off-day for the Cubs' first baseman, but he did strike out as a pinch-hitter in the eighth inning. The day off allowed Rizzo to miss Mariners' lefty Wade Miley and get some extra rest, because Chicago finishes the series on Sunday night.
Rizzo is batting .214 since the All-Star break, with three home runs, five doubles and 16 RBIs.
"He's really been needing a day," Maddon said. "We rely on him so heavily all the time, it was the right thing to do today. I don't wait until a guy gets hurt to need a day off. I'd rather be proactive with that. I put out the feelers yesterday."