The Royals also placed left-handed pitcher Danny Duffy on the 15-day disabled list.
At 38, Tejada is the Royals' oldest player and is returning to the Majors after a one-year absence. He last played for San Francisco in 2011, batting .239 in 91 games.
"He still has plenty of bat speed, he's versatile in terms of being a kid that can play third, second and first base, and shortstop. And tremendous leadership and tremendous experience," Yost said.
Tejada played for Aguilas in the Dominican Winter League and batted .284 with four homers and 19 RBIs in 34 games. He also played for the Dominican Republic in the Caribbean Series and in that country's championship run in the World Baseball Classic.
"We got great reports on him in winter ball and I wanted to see the whole package and I was very impressed," Yost said.
Tejada and Elliot Johnson are the backup infielders and Johnson also could see outfield duty. Jarrod Dyson is the reserve outfielder and George Kottaras is the second catcher.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.