CHICAGO -- Lost in the euphoric frenzy of the Chicago Cubs' recent fan convention, followed by the excitement of visiting the White House the next day, was a telling, throwaway line by team president Theo Epstein when he addressed reporters as the weekend kicked off at the Sheraton Grand Chicago.

“We went 1-for-2 in Ross signings,” Epstein quipped.

Epstein was referring to the addition of David Ross to the Cubs' front office and free-agent pitcher Tyson Ross' signing with the Texas Rangers on the same day. We could argue about which Ross would have more long-term impact on the team, but there’s little doubt that Tyson would have been more integral to the 2017 roster. In fact, he was the perfect fit, considering he is coming off an injury. A delayed start to his season would have given Mike Montgomery a real chance at the No. 5 spot in the rotation, and Ross could have been added later as a sixth starter or to replace Montgomery, if needed.

In any case, the Cubs lost out on Tyson Ross and still face depth issues in their pitching rotation. This is no small factor as spring training nears.

At the moment, Montgomery is replacing Jason Hammel in the starting rotation, and Rule 5 pick Caleb Smith is replacing either Montgomery or Travis Wood in the bullpen, depending how you view the roster. (Hammel and Wood are still available in free agency.) Those are some big shoes to fill, though the Cubs did enhance the back end of the bullpen with the additions of righties Koji Uehara and Wade Davis. Perhaps this puts the Cubs in a catch-22 with emerging lefty Rob Zastryzny.

Epstein said in early December that Zastryzny would be a depth starter for the organization, most likely beginning the season at Triple-A Iowa. Would it be more beneficial for the team if Zastryzny remained in the bullpen for the big league team? Of course, that would weaken the depth on the starting rotation, but the alternative puts a lot of responsibility on Smith and newcomer Brian Duensing. Of course, Zastryzny is still early in his career as well, so no matter how you look at it, the Cubs are thin or unproven from the left side of the bullpen.

The Cubs need to decide whether lefty Rob Zastryzny will be more valuable to the team this season as a depth starter or in the bullpen. Jayne Kamin-Oncea/USA TODAY Sports

The feeling is that the bigger concern is the starting rotation, as Jon Lester, John Lackey and Jake Arrieta are all coming off back-to-back playoff years, the most recent of which went as long as a season can possibly go. That’s not to mention the innings jump Kyle Hendricks experienced. Health and durability for yet another long season, as the Cubs attempt to repeat as World Series champions, are on everyone’s minds and invoke Epstein’s theory on the subject: When you’re rebuilding, you’re looking for ways to squeeze out a few more wins and make a playoff run. When you’re on top, you’re thinking of all the ways you could take a tumble and give back those wins. An injured rotation is the fastest way out of first place.

“Of course I still like their team a lot,” a National League Central Division scout said via text. “They’ve had no injuries. What happens if they do?”

The scout also indicated that you can ask that question of just about any contending team. The Cubs have been here before, whether it’s injuries to Mark Prior and Kerry Wood during high-expectation seasons or an entire starting staff on the disabled list in 1985, after the Cubs won a division title the season before. That brings us to the same question that was posed at the beginning of this offseason -- and even during the World Series. The day Kyle Schwarber returned was the first day anyone asked, "Where is Javier Baez going to play next year?" Replace Baez’s name with Ben Zobrist, and the question still stands.

On paper, trading one of the position players for a stud pitcher makes a lot of sense. In fact, on paper, trading Schwarber makes sense. Baez could play his best position on this team (second base), and Zobrist could play left field while the Cubs potentially get a haul for the near-MVP of the World Series. But that would be shortsighted, as Schwarber’s bat is just too good unless the Cubs were to get a true No. 1 pitcher in return.

Baez remains the best trade candidate for both sides to get real value. The Cubs have to be hesitant, though. It’s not like they have a hole in their rotation now; they just have a hole in the depth of their rotation. Is that enough of a need to trade a valuable piece from the big league team such as Baez? Probably not. That’s why the Cubs should and likely will dangle more prospects, starting with switch-hitting third baseman Jeimer Candelario.

Perhaps the Cubs will enter this season knowing they are thin in the starting rotation and will proceed mid-season in addressing that concern. Depth is needed in case of injury or in the second half of the season. If a starter goes down right away, they’ll have to react, but this is a longer-term issue. After the 2017 season, the Cubs will need some starters. Developing one from within their system always feels like it’s a year away, though Zastryzny finally became the first Epstein-era pitcher drafted by the team to make it to the big leagues. The Cubs would like a few more arms to emerge, but in the meantime, they’ll keep looking.

“Pitching depth,” Epstein said. “That’s what we’re looking for.”

It’s the same answer he gave last offseason, and somehow, the Cubs managed just fine and won the World Series. Can they do so again, or will they add more than a minor league arm to the mix?

We’ll find out over the course of the next few weeks, but for now, they’ll need their top pitchers to be the horses they were last season. There are no other options.