PORT ST. LUCIE, Fla. -- Jordan Walden, who missed the final five months of the 2015 season due to a rotator cuff injury, did not pitch as scheduled in the Cardinals' 5-5 tie with the Mets on Friday after alerting the club to "a little knot" that was causing some tightness when throwing.

Walden described the issue as "nothing serious," but given his injury issues over the past year, it is enough of a development to give the Cardinals pause. Manager Mike Matheny acknowledged that the timing of the setback is reason for concern. The club opens the season in nine days.

"We have to get him in there," Matheny said, "and see how he responds."

The Cardinals entered camp unsure exactly how much they'd be able to rely on Walden after he was limited to 12 appearances last season. That uncertainty had been fading with each subsequent appearance Walden made. In six outings, the most recent of which came on Monday, Walden had allowed no runs and two hits.

Walden said the discomfort began a couple days ago, though Matheny noted that he was alerted to the issue on Friday morning. There was also some inconsistency in the description of the injury, as Matheny understood it to be related to the reliever's damaged rotator cuff, while Walden described it as an issue with his latissimus dorsi muscle.

Walden, nevertheless, downplayed the seriousness of the setback.

"My shoulder started feeling really good, and I just think other parts of my arm weren't used to it," Walden said. "Normal stuff, nothing crazy, nothing serious. I'm happy I'm pitching in games, but this is just a little bump in the road, I guess. Nothing serious, and I'll recover."

As of now, the Cardinals have not made plans to shut Walden down or send him out for an exam.

"He's had lots and lots of rest," Matheny said. "We have to see how it responds, and we're going to need him to go out and pitch and show that it's healthy so we can figure out what to do."

With six Grapefruit League games remaining, the Cardinals will be tight on time to determine Walden's readiness for the season opener. He had pitched well enough to reclaim his spot in the bullpen. If Walden does not recover as quickly as anticipated, the Cardinals would have two bullpen openings to fill. Candidates for those spots include Tyler Lyons, Matt Bowman, Juan Gonzalez, Dean Kiekhefer, Miguel Socolovich and Sam Tuivailala.