General manager John Mozeliak was optimistic Friday that Lynn would be ready to rejoin the rotation in 15 days. The pitcher thought so, too, and believed he was set to resume playing catch in the next few days.
The 28-year-old Lynn said the forearm had been bothering him off and on since his second start of the season. The move was made retroactive to June 8.
"It's just something you try to go through as long as you can," Lynn said. "It's not getting worse, but if we can get it calmed down, we might as well do it right now."
Both Mozeliak and manager Mike Matheny believed Lynn could have pitched through the injury but did not want to risk losing him for a long time.
Going forward, Lynn said the team would try to better manage the arm to avoid a recurrence.
"We did not want to try to push through this," Mozeliak said. "Giving him a layoff will help. He's such a key part of our rotation."
Lynn is 4-4 with a 3.07 ERA in 12 starts. He has won 15 or more games in all three seasons he has been in the rotation, going 15-10 with a 2.74 ERA last year.
He has topped 200 innings each of the past two seasons, and this is his second stint on the DL, the other coming in his rookie year in 2011.
The Cardinals had a day off Thursday but opted not to move the other starters up, figuring the rest will pay off down the line.
Lyons struggled in an earlier call-up while replacing injured ace Adam Wainwright. He had a 5.54 ERA in three starts covering 13 innings. He is 5-2 with a 2.61 ERA in eight starts at Triple-A Memphis.
"Tyler has been throwing extremely well," Matheny said. "We believe he's going to be able to translate that here."
When Lyons was demoted, the team asked him to work on consistency.
"He knew exactly what he needed to work on," Matheny said. "Consistency is what separates guys that stick around here from guys who keep bouncing back and forth."