Tejada entered the season as the Cardinals' presumptive starting shortstop, but a hot start from rookie Aledmys Diaz limited his role.
"We weren't getting Ruben much work," manager Mike Matheny said. "It was different from what he thought it might be and different from what we thought it might be."
Tejada can now choose to accept the Cardinals' assignment to Triple-A or sign with another team.
Designating Tejada leaves room on the active roster for infielder Greg Garcia, who was called up on Thursday to fill in for Carpenter. Garcia went 2-for-3 with three walks and a home run in two games against the Nationals, while playing impressive defense at third base. He found out after Friday's game that he would be sticking around.
"I had these visions of, 'What can you do to stay?'" Garcia said Saturday. "Might as well try to get four hits and hit a homer and see what happens. What do you have to lose?"
Garcia made the Cardinals' Opening Day roster but was sent to Triple-A Memphis on April 17, despite hitting .600 at the time. His performance against Washington lifted his average to .615 on the season. Matheny praised Garcia on Friday, and said the infielder was making it hard for the team to return him to the Minors.
"Right off the bat, [Garcia got] us going with the two at-bats [in which] he drew the walks," Matheny said. "And then we're not even talking about a homer to the opposite gap. Just a great day."
• Matheny said injured shortstop Jhonny Peralta will likely continue his rehab assignment at Triple-A Memphis after a few games at Double-A Springfield. Matheny said it is "unlikely" Peralta will rejoin the team this week for a series in Milwaukee. Peralta has been out since March with a torn ligament in his left thumb.
Alex Putterman is a reporter for MLB.com based in Washington.