MIAMI -- It's no mystery the Marlins are in the market for an impactful left-handed hitter, and the organization just might have a secret weapon lurking in its farm system.
Second baseman Isan Diaz made big strides at the Double-A and Triple-A levels in 2018, and he wrapped up his year by playing winter ball in Puerto Rico. The 22-year-old is ranked by MLB Pipeline as Miami's No. 9 prospect, and the No. 4 second-base prospect overall.
Of all the Marlins' prospects, Diaz is regarded as the closest to being big league ready.
The Marlins consider Diaz their second baseman of the future, and his estimated time of arrival in the big leagues could hinge on how much longer Starlin Castro remains with the organization.

Castro is in the final year of his contract, and the four-time All-Star may be dealt before the July 31 non-waiver Trade Deadline. Miami is exploring trade options for Castro, but his $11 million salary makes it extremely unlikely that he will be dealt before Spring Training begins on Feb. 13 at the Roger Dean Chevrolet Stadium Complex in Jupiter, Fla.
Diaz played some third base in the offseason, but the Marlins are grooming him as their second baseman. While he is expected to start off at Triple-A New Orleans, reaching the big leagues around midseason is certainly possible.
A native of Puerto Rico, Diaz recently wrapped up winter ball for the Gigantes de Carolina squad, hitting .272/.348/.368 with six doubles, one triple, one home run and 13 RBIs in 33 games.
Acquired from the Brewers in the Christian Yelich trade last January, Diaz opened 2018 at Double-A Jacksonville before a promotion to New Orleans.

In 119 Minor League games, his slash line was .232/.340/.399 with 23 doubles, five triples, 13 homers and 56 RBIs. At Double-A, his numbers were .245/.365/.418 with 19 doubles, one triple, 10 homers and 42 RBIs. There were some growing pains at New Orleans, where his slash line was .204/.281/.358 with three homers and 14 RBIs in 36 games.
In Diaz, the Marlins feel they have a second baseman with 20-homer power, and he has shown the ability to hit the ball hard to all fields. According to Miami's internal analytics, 9 percent of the balls Diaz put in play in the Minors in 2018 had an exit velocity of at least 105 mph. The MLB average is 7 percent.
More than just the numbers, the Marlins didn't hesitate to expose Diaz to higher-level pitching, and he saw more of it in the offseason.
When you add in 33 games in the Puerto Rican Winter League, Diaz appeared in 152 total contests, with 545 combined at-bats. That gave Diaz a sampling of what the rigors would be like over a full Major League season. Additionally, Diaz participated in a tournament with the Puerto Rican national team.

The Marlins are giving Diaz even more preparatory experience before camp begins.
Diaz, outfielder Monte Harrison, the Marlins' second-ranked prospect, and right-hander Jordan Yamamoto (No. 17) have been invited to the Rookie Career Development Program, which is being held this week in Miami.
Prospects from all 30 big league clubs are invited to the annual event that features seminars and guest speakers.
Harrison, like Diaz, is expected to open the season at New Orleans. How quickly he progresses to the big leagues depends on how he continues to refine his approach at the plate, while demonstrating he can make consistent contact.