"It gives us more freedom to do things in the latter part of the game," Cubs manager Joe Maddon said. "You've seen us pull catchers for different manuevers. 'Fed' has forced our hand to do this because he's played so well and he looks so good. That's how we chose to do it. It can change, but for right now, we thought it was the right thing to do."
Federowicz, promoted from Triple-A Iowa when Montero was injured, was 4-for-20 in seven games so far.
• Montero: Arrieta throws 'Hall of Fame pitches'
To make room on the roster, Ryan Kalish was designated for assignment. The outfielder was 2-for-7 with two RBIs in seven games, and had batted .368 with four doubles and two triples in 20 games with Triple-A Iowa.
Montero was 2-for-10 in three games with Triple-A Iowa as part of his rehab assignment. He caught two of the games, and was the designated hitter in the other one.
"The first day, I was a little skeptical about blocking, but I got to block a lot of balls," Montero said. "I felt pretty good blocking, and that was the turning point and I felt like I was good to go."
Montero, who was batting .208 in 13 games before he was sidelined, said he has added more core exercises in hopes of avoiding any further back problems.
"I have to still do it and stay on top of that for the rest of the season, and for the rest of my career," he said.
The Cubs were a little concerned about overworking Ross, 39, who has said he will retire at season's end. On Friday, Ross hit a three-run homer in a win over the Pirates.
"I think we're going to give him a qualifying offer," Montero joked with Ross.
• Matt Szczur, on the disabled list with a right hamstring strain, has increased his activities and was making progress. He is eligible to come off the DL on Wednesday.
• Maddon doesn't believe in appointing a team captain, saying it's an "organic situation." He does have his "lead bulls," who are players he relies on to keep the clubhouse and players in order.
"There's no 'C' on anybody's chest -- no 'L.B.' on anybody's chest," Maddon said. "I like the fact that it's spread out among them."
• Addison Russell, who is the youngest player on the Cubs at 22, entered play Saturday leading the Cubs in batting with runners in scoring position at .368.
"If you're talking about guys who are good in clutch moments, it's because they're able to stay in the present tense," Maddon said.