Thompson was optioned to Triple-A Lehigh Valley on Thursday, Matt Gelb of The Philadelphia Inquirer reports.
Thompson is heading back to Triple-A after a rough outing earlier this week. The Phillies have an off-day Monday, which could allow them to bring up a reliever temporarily and skip the need for a fifth starter. Mark Leiter, Zach Eflin and Ben Lively (knee) are the likely options to eventually fill the rotation opening.