Tejada issued an apology through the Major League Baseball Players Association, and Royals players expressed surprise and praised him as a good teammate.
Yahoo! Sports' Jeff Passan reported that because Tejada had tested positive under MLB's amphetamine policy earlier in his career, he was subject to a 25-game ban for a second positive, found in a test this season. A third positive test followed and called for an additional 80-game suspension, totaling 105 games.
The 105-game suspension is the third-longest ever levied by MLB, behind the 211-game penalty Alex Rodriguez is currently appealing and Steve Howe's 119-game ban in 1992. With 41 games remaining this year, Tejada's suspension would carry over through the first 64 games of the 2014 season, but there were reports the 39-year-old was considering retiring.
Tejada's season with the Royals was effectively ended anyway on Wednesday when he was placed on the 60-day disabled list with a strained right calf sustained on Aug. 10.
In his statement, Tejada explained that he took a banned substance while re-applying for a Therapeutic Use Exemption. According to multiple reports, including one from USA Today, Tejada's exemption expired on April 15.
MLB issued a record 116 Therapeutic Use Exemptions for attention deficit disorder between the beginning of the 2011-12 offseason and the end of the 2012 postseason, according to the most recent annual report from MLB's Joint Drug Prevention and Treatment Program's Independent Program administrator.
"I apologize to my teammates, the Royals organization and to the Kansas City fans," Tejada said in the statement. "I have a medical condition that requires medication to treat. I took that medication while re-applying for a Therapeutic Use Exemption. Under the requirements of the Joint Drug Program, I made a mistake in doing so."
Royals general manager Dayton Moore declined direct comment on the decision.
"There's a program in place and there's consequences for action, so there's nothing I can really say. It's Major League Baseball's deal and there's nothing we can really comment on," Moore said. "It's just unfortunate."
"He was a great teammate," manager Ned Yost said before Saturday night's game against the Tigers. "He was awesome when he was here with us, and we just found out about it ourselves. It doesn't have much of an impact for us because he was already out for the year with the calf thing, but Major League Baseball has a drug program in place and we go with it."
Tejada, a six-time All-Star who won the 2002 American League MVP with the A's, was signed as a Minor League free agent by the Royals last winter on New Year's Eve. In 2012, he had re-signed with one of his former clubs, Baltimore, and played just 36 games for Triple-A Norfolk before leaving the organization. But he played in the Dominican Winter League with Aguilas and impressed Royals scouts enough that he was signed.
Touted as a positive clubhouse influence on younger players, Tejada reported to Spring Training in great shape and regularly held pre-workout gatherings with other players.
"He was a great guy all the time," shortstop Alcides Escobar said. "He taught me and everybody in here. Maybe he made a mistake, I don't know anything about that. He was really a good guy, a good teammate, one of the best guys in here."
"It's a big blow," third baseman Mike Moustakas said. "Miggy is a great guy, a great teammate. We're going to miss him. … He's a great leader and a great mentor to me. He's helped me out a lot."
Tejada made the club as a backup infielder. Early in the season, he played little, but as injuries and slumps took their toll, he got more playing time. From July 3 to Aug. 10, the day he was injured, he was in 24 games including 22 starts -- mostly at second base but some at third base -- and batted .305 with 11 RBIs. He also fielded well.
Overall for the Royals, he played 53 games with a .288 average (45-for-156) with five doubles, three homers, 20 RBIs and a .317 on-base percentage.
"Tejada is one of the best teammates I've been around. He was amazing for our clubhouse," pitcher James Shields said. "He did everything he could on the field. He showed up every day. It definitely surprises me, for sure.
"Every day he came in, he was a great teacher. He helped out a lot of our young guys, not only our Latin guys, but everybody. He really taught a lot these guys how to play the right way as far as how on the field goes."
Shields was asked about the message that MLB was sending by penalizing former MVPs such as Tejada, Ryan Braun and Rodriguez.
"It doesn't matter if you're MVP or king of the world," Shields said. "If you're going to do things that are illegal, you're going to get caught for it and you're going to get suspended. It's a shame because I really like him a lot as a teammate. He was so much fun to be around, every day. He came in here with a smile, every day. He really lifted our team up."
"It was a surprise," pitcher Jeremy Guthrie said. "I think ultimately we enjoyed our time with him, as a friend, as a teammate. I had a chance to play with him also in Baltimore for a couple of years. I think he added a lot to our team.
"On the drug side of it, I think it's another positive sign that the testing continues to work and that those players who commit infractions against the drug policy are being penalized accordingly. I think that's the point of it, I think that what all players and fans alike are hoping for. It's unfortunate when it's a friend of yours and a teammate but the testing is there for a purpose and this is another indication that it's working and serving its purpose."