The Astros' rotation depth for next season has been dealt a tough blow. Prospect Corbin Martin underwent Tommy John surgery on Wednesday, Astros general manager Jeff Luhnow told reporters (via Chandler Rome of Houston Chronicle). That means Martin is done for the 2019 season and will miss a chunk of the 2020 season as well. 

Martin, 23, was ranked as the 78th best prospect in baseball prior to the season by Baseball America. He struck out 45 hitters against 18 walks with a 3.13 ERA and 1.37 WHIP in 37 1/3 Triple-A innings this season. He made five starts for the Astros and pitched to a 5.59 ERA. He allowed far too many baserunners (1.81 WHIP), though he did strike out 19 hitters in 19 1/3 innings. 

The Astros are fine without Martin this season, but moving forward is when he would become an integral part of the equation. Gerrit Cole and Wade Miley are both set to hit free agency after the season. So is Collin McHugh. Should both walk, the Astros are looking at something like this in the rotation without help from outside the organization: 

Getting McCullers back from Tommy John surgery certainly helps matters, but there's really only one guy listed there who doesn't come with questions and that's Verlander. And he'll be 37 years old. 

It'll be interesting to see how things unfold with this group moving forward, but one thing we know right now is Martin won't be available for the early part of 2020.