CHICAGO -- David Freese's production hasn't trailed off substantially of late. But that is not stopping manager Mike Matheny from being proactive about getting his third baseman some rest.

Freese, who is nearing the end of his first healthy season in the Majors, has already appeared in 136 games after playing barely a full season's worth in the previous two years combined. Injuries kept Freese off the field for large portions of the 2009-11 seasons.

That's enough of a reason, Matheny said, to watch closely for fatigue. Freese wasn't in the Cardinals' lineup for Friday's opener with the Cubs.

"There are times you can see by his movements that he's getting worn down," Matheny said. "Could we throw him out there and push him and grind him good? There's no question we could. But is that the best thing for him and the best thing for us? I think history has shown us that's probably not the case."

Matheny didn't rule out resting Freese for more than just one day, though the urgency to reel off wins could trump that this late in the season. The Cardinals do have the benefit of being able to start Matt Carpenter in Freese's place while not taking too substantial of a hit on the defensive or offensive end.

Freese has hit .295 this season. Carpenter, in 104 games, is batting .297.

Workload of Motte, Boggs a concern for Matheny

CHICAGO -- Fernando Salas has worked the Cardinals out of two critical jams within the past week, both times setting the club up for a win. With the back end of the St. Louis bullpen hampered by workload concerns, Salas could be thrust into critical late-inning situations during this weekend's series in Chicago.

Manager Mike Matheny wouldn't label Mitchell Boggs or Jason Motte unavailable on Friday, but he did admit that he would show substantial hesitation in using either, even in a close game. Motte has pitched in five straight games, with one team off-day the only interruption in that stretch. Boggs pitched in all three games of the Cards' last series after being sidelined just before with lower back tightness.

Both Boggs and Motte insist -- publicly, at least -- that they are feeling nothing more than typical late-season fatigue. But there is concern about pushing them any further right now.

"I'm concerned about [Motte] and Boggs, both," Matheny said of his closer and setup man. "We're going to have to see how they feel today, and [how] the game situation plays out. You just feel your way through."

Even seventh-inning reliever Edward Mujica has shouldered a substantial workload as of late, putting his availability into question, too.

Salas, on the other hand, is relatively fresh, having pitched just four times since Sept. 8. He has been scored upon in just two of his last 20 appearances and has plenty of past experience pitching late in ballgames. Salas saved 24 games in 2011.

The right-hander's last two appearances have been among his biggest of the season. With the Cardinals threatening to fall behind Los Angeles in the National League Wild Card race last Sunday, Salas recorded two outs with the potential winning run standing at third in the 10th. He then preserved a one-run lead on Thursday by striking out two with the bases loaded.

"He's making his pitches. He's hitting his spots," Matheny said of Salas. "There's a little more life on the ball. Why? I don't know. We went through some health things early and tried to fight through it. He just wasn't himself. But he does look more like the Fernando Salas we've seen in the past."

Westbrook pushes bullpen session to Saturday

CHICAGO -- Scheduled to throw off the mound on Friday, Jake Westbrook pushed that session back a day after dealing with some minor discomfort in his right side following a bullpen session on Wednesday.

Instead of moving forward as scheduled on Friday, Westbrook only threw on flat ground. Afterward, he reported feeling much better than he had the day before.

Westbrook has already missed two starts due to a right oblique strain. His hope was that he would be cleared to return after throwing a second bullpen session. Westbrook said this one-day setback hasn't changed that expectation.

If Saturday is indeed the last step in the right-hander's recovery, the Cardinals could plug Westbrook into the rotation during the team's three-game series in Houston, which begins on Monday.

Because Westbrook's status remains fluid, the Cardinals have not announced their rotation beyond this weekend. Every expectation is, though, that Lance Lynn will stay on turn and pitch Monday's series opener. Lynn threw his scheduled in-between starts bullpen session on Friday.

Worth noting

• Left-hander John Gaub, whom the Cardinals selected off waivers from the Rangers in June, was outrighted off the club's 40-man roster on Friday in order to open a spot for Chris Carpenter. Carpenter came off the 60-day disabled list to start the opener vs. the Cubs. Gaub finished the year with Triple-A Memphis, where he posted a 6.88 ERA in 33 relief appearances.

• With four saves in the team's last four games, Motte became the first Cardinals closer with that many consecutive saves since Lee Smith recorded a save in five straight games in June 1993.

• Memphis general manager Ben Weiss has been named the Pacific Coast League executive of the year, an honor voted upon by the other PCL GMs. Weiss has served as Memphis' GM since August 2009.