"Everyone at the Red Sox was shocked to hear of Daniel's tragic passing," Red Sox president of baseball operations Dave Dombrowski said in a statement. "To see the life of a young man with so much promise cut short is extremely saddening for all of us. On behalf of the Red Sox organization, I would like to extend our deepest sympathies and condolences to Daniel's family."
It had not been made public that Flores had cancer until after his death. The Red Sox didn't disclose the type of cancer out of respect for the wishes of the Flores family.
Flores had been undergoing cancer treatments at Massachusetts General Hospital in recent weeks.
The news came one day after former star Major League pitcher Roy Halladay died in a plane crash.
Assistant general manager Eddie Romero, who helped lead the effort to sign Flores, also released a statement.
"Every member of our organization who got to know Daniel absolutely loved him," said Romero. "He was energetic, hard-working and genuinely selfless, always with a smile on his face. He cared for his teammates and was a natural leader. I'm at a loss for words today. Daniel was an impressive young man with limitless potential, and his life was cut far too short.
"My condolences go out to Daniel's mother and sister. Though with us for a short time, Daniel will always be a part of the Red Sox family."
Flores idolized Royals catcher Salvador Perez and had the chance to meet him a few times. Flores hoped to one day play on the same Major League field as Perez, who helped the Royals win the World Series in 2015.
Flores was ranked as the fifth-best prospect in Boston's farm system by MLBPipeline.com.
Some scouts felt Flores was the best international prospect available last summer, and the Red Sox graded him as an elite defender with promising raw power. A switch hitter, Flores was projected to do damage from both sides of the plate.
Combine those traits with footwork, a strong arm, a sound release point and an impressively seamless transfer for a 17-year-old, and the Red Sox were sure Flores was the player to target as their top international signing.
Boston was excited to watch Flores develop, and he was slated to play in the Dominican Summer League in 2018.
One thing that impressed the Red Sox about the strides Flores made defensively in such a short amount of time, is that the prospect started out as a shortstop.
In Venezuela, Flores was trained by former Blue Jays Minor League infielder Jose Salas Jr. Flores moved to catcher at Salas' Puro Beisbol academy in Caracas and developed into the top amateur catcher in Venezuela prior to signing with the Red Sox.
MLBPipeline's scouting report on Flores
After the Red Sox spent heavily on the 2014-15 international amateur market for talents such as the since-traded Yoan Moncada and Anderson Espinoza, baseball rules prohibited them from spending more than $300,000 on an individual player in the next two signing periods. Freed from those restrictions in 2017, Boston landed Flores, whom some teams considered the best player available. His all-around potential as a catcher earned him a $3.1 million bonus out of Venezuela.
Flores is one of the best defensive catchers amateur scouts have seen in years, earning comparisons to the likes of Austin Hedges. He has a well above-average arm, the product of plus arm strength, a quick release and impressive accuracy. He also receives and blocks well, giving him all the ingredients to develop into a Gold Glover.
A switch-hitter, Flores is better from the right side of the plate and is still honing his lefty stroke. He has the chance to hit for average and power as he gets stronger, and he already shows some ability to drive the ball during batting practice. The only tool he lacks is speed, as is the case with most catchers.