McClanahan was pulled after three innings in Friday's start against the Mariners after his back flared up, Marc Topkin of the Tampa Bay Times reports.
McClanahan allowed four earned runs on five hits and three walks, and the Rays initially claimed the quick hook was a result of ineffectiveness rather than injury. However, after the game, manager Kevin Cash admitted that McClanahan's back became an issue. Further testing will be done, but Cash noted that a stint on the injured list is a possibility.