McClanahan (left forearm tightness) shut down for season

6:04 PM UTC

ST. PETERSBURG -- has been shut down for the rest of the MLB postseason, Kevin Cash announced Sunday, leaving the Rays without one of their best pitchers as they chase their first World Series in franchise history.

This was the biggest question looming for the Rays ahead of the AL Championship Series, which begins Monday at Tropicana Field. McClanahan has been out since Sept. 3, when he left a start against the Rangers after feeling tightness in his left forearm.

There had still been some small level of hope that McClanahan could return for the ALCS or World Series, which could have been valuable as the series expands to seven games and pitching is stretched even thinner. The Rays are still in very good hands to open the series, though, with Drew Rasmussen officially lined up to start Game 1.

Rasmussen is coming off an All-Star season, and he is expected to receive votes high on AL Cy Young Award ballots behind the consensus favorite, Cam Schlittler of the Yankees. The 31-year-old Rasmussen posted a 2.67 ERA over 172 innings this season. He is coming off one of the finest performances of his career, in Game 1 of the ALDS against the Yankees, when he carried a no-hitter into the eighth inning and struck out 10 during Tampa Bay's 1-0 win.

Looking ahead in this ALCS behind Rasmussen -- and without McClanahan in their plans -- the Rays are likely to utilize a four-man rotation. Freddy Peralta and Nick Martinez are expected to pitch behind Rasmussen, then either Griffin Jax or Ian Seymour will fill in the fourth spot, with the other working out of the bullpen.