ST. LOUIS -- As part of the countdown to the start of Spring Training, cardinals.com continues its series of stories designed to examine various issues, address important questions and spotlight players who could be critical to the Cardinals' success in 2016.
After highlighting a group of bounce-back candidates and some new faces, it's time to identify some prospects to keep an eye on this spring. Considering only those invited to Major League camp, here are five worth watching:
• Comeback candidates | Newcomers
LHP Marco Gonzales: Gonzales is the only one on this list who has appeared in the Majors, though because of service time, he remains rookie eligible. The lefty starter ranks third on MLB Pipeline's organizational prospect list and could pitch his way onto the Cardinals' Opening Day roster if an opening materializes in the rotation or the club needs additional bullpen help. Gonzales made one big league appearance in 2015, due to ongoing left shoulder issues.

OF Charlie Tilson: Added to the 40-man roster in November, Tilson gives the Cardinals additional outfield depth, following the winter departures of Jason Heyward, Jon Jay and Peter Bourjos. Tilson, No. 7 in MLB Pipeline's Cardinals prospect rankings, is likely to open the season at Triple-A Memphis, but he could make a Major League impact sometime around midseason. He has above-average speed and can handle center field capably.
RHP Luke Weaver: Weaver won't be competing for a big league roster spot this spring, but he has been invited to Major League camp for the first time. A first-round Draft pick in 2014, Weaver posted a 1.62 ERA in 19 High-A starts last season. He finished his season in the Arizona Fall League and ranks eighth on the club's prospect list, per MLB Pipeline. Weaver is projected to open '16 in Double-A Springfield's rotation.
SS Aledmys Diaz: Diaz's strong finish in 2015 prompted the Cardinals to put him back on their 40-man roster, after removing him from it midseason. It's been almost two years since the Cuban shortstop signed with the Cards, and this could be the year he finally makes a big league impact. Diaz hit .380 while playing the final 14 games of last season in Triple-A and took that momentum to the AFL. With the Cardinals lacking in shortstop depth, he could become an important piece in '16.

C Carson Kelly: Kelly, two years after converting to catcher, won a Minor League Gold Glove award at the position last season. His bat hasn't come along as quickly, but the 21-year-old is still developing in many ways. He ranks 17th on the organization's MLB Pipeline list and will benefit again from being able to work alongside the team's Major League catchers in camp. As the Cardinals consider options for Yadier Molina's eventual heir, they hope Kelly pushes himself into that mix.