Who will take Zimmermann's innings in the Nationals rotation?

Now that right-hander Jordan Zimmermann has moved on to the Detroit Tigers, the Nationals must figure out how they will replace the coveted starter.

Zimmermann tossed 201 2/3 innings in 2015, compiling a 13-10 record with a 3.66 ERA. He matched Max Scherzer with 33 starts and was second on the team for innings pitched, 27 innings less than Scherzer.

With right-hander Doug Fister also not returning, the Nationals must look to find a pair of starters.

Right-hander Joe Ross would be the most likely to take over the No. 4 or No. 5 slot. He is 22 and made an impressive debut with the Nationals in 2015. Ross made 13 starts and appeared in 16 games, twirling 76 2/3 innings. Even if he doubles his innings in 2016, he still would not be able to reach 200-plus innings, which is probably too much to ask from a young pitcher in just his second major league season.

Right-hander Taylor Jordan has made 15 starts with the Nationals the past three seasons, but only one last season. He could be a candidate with a very good spring training, but doesn't have the experience at this level to lock down the No. 5 starting spot.

Right-hander A.J. Cole had a difficult start with the Nationals last season, but has the stuff if he can learn to command all of his pitches in various counts. His average exit velocity on his four-seam fastball is 95.18 mph. The major league average is 89.87 mph according to MLB.com.

The Nationals could also go back to right-hander Tanner Roark. Roark won 15 games in 2014, but was relegated to the bullpen last season. He ended up returning to the rotation in 2015 when needed to make 12 starts and pitch a total of 111 innings. He is the most logical fifth starter if the season started today, with Ross the No. 4.

Is Roark's value bigger in the 'pen or as a starter? That question will be answered the next few weeks as we see what the Nationals do in free agency because the bullpen is a bigger need right now than the starting five.

Or is there an outside solution?

In years past, president of baseball operations and general manager Mike Rizzo has found Edwin Jackson, Dan Haren and Fister. Might he look for a big splash in the free agent market again? Or would Mat Latos, Wei-Yin Chen, Yovani Gallardo and others be possibilities? It may very well be the solution they will need to pursue, getting a veteran in to shore up the No. 4 spot.

And then there is Lucas Giolito.

The first-round selection from 2012 is only one year younger than Ross. The Nationals worked very hard with Giolito on his demeanor late in games and how he can pitch his way out of jams after the fourth and fifth innings, when the other team has seen your stuff a couple of times. And speaking of stuff, the kid has it.

He could display how good he is in spring training again and build closer to an opportunity with the club as a starter, maybe even as early as June or July. Rizzo has shown in the past he is not afraid to promote his starters from Double-A. Giolito made 19 starts and tossed 111 innings with three minor league teams in 2015. He will be well over three years removed from Tommy John surgery when the 2016 season arrives.