Francis (3-7, 5.67 ERA) matched the club record last season with 17 wins and won two postseason games to help the Rockies reach the World Series. This season, however, Francis did not earn his first win until his ninth start, and his ERA has not been below 5.01.
It's the first career DL trip for Francis, who decided after his most-recent bullpen session to have an MRI. That occurred on Wednesday.
Francis said it didn't hurt during innings, but he'd feel it while loosening up for later innings or the day after the game. Certain motions, he said, give him discomfort.
"It's something I've felt before -- not during the season, but during the offseason lifting weights or something like that," said Francis, who said he will rest for a couple of days before throwing.
Rockies manager Clint Hurdle said he and Francis have discussed whether the inflammation has led to an inconsistent arm slot and fluctuating fastball velocity. Francis admitted he has "been in the training room every day for the last little while."
A location pitcher, Francis relies on repeating his delivery and a consistent motion. The steadiness helped him win 44 games from 2005-07. No lefty won more during that stretch.
However, this year, the Rockies are 5-12 in Francis' starts. That's one of the reasons they entered Wednesday night's game with the Padres 18 games under .500. The inconsistency of his performance, he said, has as much to do with his going on the DL as the discomfort in his shoulder.
"I can take a step back and try to evaluate what I've done and what I need to do to get it over with," Francis said. "If I was 9-4 instead of 3-7, I don't know if we'd be having this conversation."
Hurdle said putting Francis on the DL, which will keep him out of action until after the All-Star break, could mean a chance to regain health and consistency.
"He's all about grinding, putting his head down, going hard, and this is part of the game, but that's one of those tough decisions and conversations you have to have," Hurdle said. "Let's talk about what we've tried, what has worked, what hasn't worked, where you feel like you might be hung up. This is the course that has taken."
Thomas Harding is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.