The team announced the moves Tuesday, a day after coach Pat Shurmur said Flowers would either be traded or waived within 24 hours.
Flowers was the ninth pick overall in the 2015 draft. He never lived up to expectations. The Miami product was moved from left to right tackle this season after free agent Nate Solder was signed. He ended up losing that job to Chad Wheeler after two games.
The Giants, who face the Philadelphia Eagles on Thursday night, also signed kicker Marshall Koehn to their practice squad. Placekicker Aldrick Rosas has a sore quad and his status for Thursday is uncertain.
Shurmur said Tuesday that Rosas' injury is improving.
Mihalik played in 15 games for the Detroit Lions in 2017, starting twice. He has been on the Giants practice squad since Sept. 13.
Koehn was with the Giants from Jan. 1 until his release on Sept. 1. He has played in one NFL game, for Cincinnati at Jacksonville on Nov. 5. He made his only extra point attempt, and had one touchback on two kickoffs.
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