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Asked how long that might be, Matheny responded: "We don't know."
Waldron, a non-roster invitee to Major League camp, missed his bullpen session on Saturday, the third day of Spring Training for Cardinals pitchers and catchers.
Waldron, 26, made 46 appearances for the Cardinals' Triple-A affiliate last season, and he was 4-6 with a 4.74 ERA and 1.28 WHIP over 76 innings. Prior to that, he spent five years pitching in the Pirates' organization.
Waldron did throw off the mound on Thursday, the first official day of Spring Training, and he was briefly spotted on the field Saturday during the team's early work. However, by the time his throwing group -- which included Seth Maness, Miguel Socolovich and Trey Nielsen -- arrived at the bullpen mound, Waldron had slipped away.
Waldron is the first spring setback for the Cardinals, whose other 30 healthy pitchers all remain on schedule.
Barry M. Bloom is a national reporter for MLB.com and writes an MLBlog, Boomskie on Baseball. Follow @boomskie on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.