The incident early today close to a protest site will hasten fears that the country's political crisis could lead to a serious outbreak of violence.
The Erawan medical centre said a 31-year man was killed with wounds to his torso.
Protesters are seeking to topple prime minister Yingluck Shinawatra ahead of elections scheduled for February 2.
Clashes on Thursday killed two people in the capital as protesters sought to disrupt preparations for the polls, which surveys suggest Ms Yingluk will win easily.
COMMENT RULES: Comments that are judged to be defamatory, abusive or in bad taste are not acceptable and contributors who consistently fall below certain criteria will be permanently blacklisted. The moderator will not enter into debate with individual contributors and the moderator’s decision is final. It is Belfast Telegraph policy to close comments on court cases, tribunals and active legal investigations. We may also close comments on articles which are being targeted for abuse. Problems with commenting? email@example.com