SEATTLE — Bryan Woo, the Mariners’ All-Star starter, was left off the team’s roster for the American League Division Series, a clear indication that he has not fully recovered from a pectoral injury.

The Mariners will start George Kirby and Luis Castillo, respectively, in the first two games against the Detroit Tigers and are expected to go with Logan Gilbert on the road in Game 3. Woo’s absence means Bryce Miller will act as the fourth member of their rotation in the best-of-five series, though he might also be used out of the bullpen.

Woo, 25, had a breakthrough season this year, going 15-7 with a 2.94 ERA in 30 starts. But he exited his Sept. 19 start in Houston after a few warmup tosses at the start of the sixth inning and was diagnosed with right pectoral inflammation.

The Mariners, who won the American League West for the first time in 24 years and earned a first-round bye, were hopeful that Woo could get healthy by the start of the playoffs, but he will miss at least their first round.

Woo took what appeared to be a big step Thursday, throwing a higher-intensity bullpen session and then pitching one simulated inning against Mariners hitters. Afterward, he expressed optimism in his progress, telling reporters: “I’m still not where I want to be in terms of game speed of everything. But in terms of how everything has progressed, I’m happy with it, considering that a week ago I wasn’t even throwing yet. And then a week from now, hopefully we’ll be in a better spot.”

The Mariners hope to have Woo available for the AL Championship Series, should they advance.