HOUSTON -- When your starting rotation has lost Dallas Keuchel, Charlie Morton and Gerrit Cole to free agency in the span of two offseasons, attrition is to be expected. No one is going to feel sorry for the Astros, though, with Justin Verlander and Zack Greinke at the ready, but there’s uncertainty near the bottom of the rotation entering 2020.

Verlander, who won the 2019 American League Cy Young Award, and Greinke, who went 8-1 in 10 regular-season starts last year after being traded to Houston, are a formidable 1-2 punch. And the return of Lance McCullers Jr. from elbow surgery should help soften the blow of losing Cole to the Yankees. Beyond that lies the biggest question for the Astros entering spring camp next week:

Who will be the fourth and fifth starters?

Before we answer that, let’s address the return of McCullers. He underwent Tommy John surgery after the 2018 season and rehabbed all of last season and will return as the presumptive third starter. He’s completely recovered entering camp, but how much of a workload will he be able to endure entering 2020? It’s difficult to imagine him throwing beyond 150 innings, but new manager Dusty Baker might have a hard time keeping the ball out of his hands.

“We need McCullers back badly and have him a full year,” Baker said. “I'm sure he's raring to go and, hopefully, will make it to a full year. We've got a couple surprises in the bullpen, the Minor Leagues, which we don't know yet. And this club always does something at the [Trade Deadline] to try to shore up.”

The candidates for the final two spots include familiar names -- Josh James, Jose Urquidy, Brad Peacock and Framber Valdez -- up-and-coming prospects -- Forrest Whitley, Bryan Abreu and Cristian Javier -- and a fresh face in Austin Pruitt, who was acquired in a trade with the Rays last month.

Urquidy has a leg up for the fourth spot considering the fine work he turned in last year, coming out of nowhere to post a 3.95 ERA in nine games (seven starts) late in the regular season and rising to the challenge with five scoreless innings in his Game 4 World Series start at Washington.

The fifth spot will depend on health, performance and style, depending on what Baker and new general manager James Click prefer. The safe bet is Peacock, who started last year in the rotation before moving to the bullpen. He has been moved between the rotation and bullpen so much the last few years, he could pitch comfortably in any role.

Valdez had a few shots in the rotation last year but struggled mightily with his control. So did the hard-throwing James, who walked 35 batters in 61 1/3 innings, mostly in relief, and wound up being sent to Florida during the season to refine his delivery. The plan was to stretch him out to be a starter this spring.

Pruitt, 30, adds some experienced depth. He made 67 appearances for Tampa Bay from 2017-19, including 10 starts, and posted a 4.87 ERA. He split last season between Triple-A Durham and the Major League club, with a 5.40 ERA in 18 appearances (six starts) for Durham and a 4.40 ERA over 14 games (two starts) for the Rays.

Like Peacock, Pruitt could move between the bullpen or rotation as needed.

A promising scenario for the Astros, though, is if one of the kids flourishes. Whitley is the only Astros prospect ranked in MLB Pipeline’s Top 100 (No. 19) and has had repeated setbacks the last two years. He trained in Arizona in the offseason to decrease distractions and improve his focus. Is this the year he finally puts it together?

While Whitley remains the Astros’ top prospect, Abreu and Javier are on the come. The 22-year-old Abreu was electric last year in his first taste of the big leagues, with 13 strikeouts in 8 2/3 innings. Javier was added to the 40-man roster after being named the team’s Minor League Pitcher of the Year. The 22-year-old averaged 13.5 strikeouts per nine innings last year at three Minor League levels and has plus command.