Mengden signed a contract with the CTBC Brothers of the Chinese Professional Baseball League in Taiwan on Tuesday.
Mengden signed a minor-league contract with the Nationals on Sunday, Robert Murray of FanSided.com reports.
Mengden re-signed with the Royals on a minor-league contract Wednesday.
Mengden was designated for assignment by the Royals on Friday.
The Royals selected Mengden's contract from Triple-A Omaha ahead of his scheduled start Thursday against the White Sox in Chicago.
Mengden is expected to have his contract selected from Triple-A Omaha to start Thursday against the White Sox, Anne Rogers of MLB.com reports.
Mengden was outrighted to Triple-A Omaha on Saturday.
Mengden's contract was selected by the Royals on Monday.
Mengden signed a minor-league contract with the Royals on Tuesday.
Mengden signed a one-year, $725,000 contract with the Korea Baseball Organization's Kia Tigers on Dec. 29, the Associated Press reports.