ST. LOUIS -- Another round of roster decisions looms for the Cardinals, who have until 7 p.m. CT on Monday to protect eligible players from the Rule 5 Draft by placing them on their 40-man roster.It's an annual exercise of risk and projection for clubs given the limited number of

ST. LOUIS -- Another round of roster decisions looms for the Cardinals, who have until 7 p.m. CT on Monday to protect eligible players from the Rule 5 Draft by placing them on their 40-man roster.

It's an annual exercise of risk and projection for clubs given the limited number of roster spots they have available. The Cards have five openings on their 40-man roster, though they'll also need some of that roster space for acquisitions this offseason.

Players who signed at the age of 18 or younger become eligible for the Rule 5 Draft after five seasons. Those who were 19 or older have to be protected within four seasons. Any such player left off the roster becomes available to the other 29 teams in the Rule 5 Draft, which, this year, falls on Dec. 14.

While the Cardinals benefited from the Rule 5 Draft two years ago with their selection of right-hander Matt Bowman , they've also recently experienced some losses. The Padres plucked an unprotected Luis Perdomo from the Cards in 2015 and then dipped into St. Louis' system again last year to take Allen Cordoba .

The Padres kept both on their 25-man roster the following season to secure the permanent rights to the player.

The moves caught the Cardinals by surprise given that neither player had ascended beyond the Class A level at the time of their respective selections. But as a club in the midst of a rebuild, the Padres had the luxury of manipulating their roster to retain both.

That strategy has forced the Cards to rethink who they protect and more equally weigh future potential with proximity to the Majors.

There are more than 50 players in the organization who would be eligible for the Rule 5 Draft if not protected. Here are a few who stand out:

The top prospects: Three players on St. Louis' Top 30 Prospects list -- Tyler O'Neill (No. 4), Austin Gomber (No. 15) and Oscar Mercado (No. 18) -- fall into this mix, and all three are expected to be added to the 40-man roster by Monday's deadline.

The Cards acquired O'Neill in a non-waiver Trade Deadline swap with the Mariners last July, and they remain intrigued by the outfielder's power potential. Gomber, a left-handed starter, had a strong year in Double-A and could make a push for a big league roster spot in 2018. Mercado, a converted outfielder, followed a breakout season in Double-A with a standout showing in the Arizona Fall League.

Eligible yet again: Corner infielder Patrick Wisdom may present the most intriguing case. He has been eligible and passed over in the Rule 5 Draft twice already, but Wisdom is coming off a year in which he slugged .507 with 25 doubles, 31 homers and 89 RBIs for Triple-A Memphis. The Cardinals considered him for a big league callup at various junctures throughout the season.

Working against Wisdom, however, is his age. At 26, he no longer dents prospect lists, and the Cardinals have others ahead of him on the depth chart. But if Wisdom is not protected again, it seems likely another team would finally take a chance on him.

Other notable names: Pitchers Matt Pearce, Trey Nielsen, Andrew Morales, Kevin Herget and Daniel Poncedeleon all reached Triple-A in 2017. Poncedeleon's time there, though, was cut short as he required head surgery after being struck by a line drive in early May.

Two other players the Cardinals were contemplating as adds -- first baseman John Nogowski and pitcher Arturo Reyes -- gave the organization additional time for evaluation by participating in the AFL. Neither posted strong numbers.