The American League playoff picture, and particularly the tight AL West race, may have received a massive variable Friday night.

Mariners ace Bryan Woo left the 4-0 win over the Astros with pec tightness and is “likely” set to undergo an MRI exam on Saturday, according to Seattle manager Dan Wilson.

The Mariners lead the Astros by one game in the division and are tied with the Tigers for the No. 2 seed, which comes with a bye.

“Obviously concerned in some ways but I think in other ways, Bryan’s a tough cookie and it was smart that he let us know and there was no reason to push it and I think we’ll just find out (Saturday),” Wilson said after his team improved to 85-69. “Too many unknowns at this point.”

Woo is one of the AL’s best starters, and his five shutout innings Friday improved

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