In terms of high-level pitching prospects, the Seattle Mariners didn’t have much depth in their farm system as it was.

And now their highest-ranked pitcher, 19-year-old right-hander Sam Carlson, announced he will undergo season-ending Tommy John Surgery to repair his right elbow. He could miss much of the 2019 season as well.

The Mariners drafted the 6-foot-4 Carlson in the second round out of Burnsville, Minnesota, in last year’s draft. Typical recovery from Tommy John is 12-15 months to repair a torn ulnar collateral ligament.

He’s considered the Mariners’ No. 3 overall prospect by Baseball America, just behind 2016 No. 1 pick, outfielder Kyle Lewis, and last year’s top draft pick, first baseman Evan White. Julio Rodriguez, a 17-year-old outfielder and international signee, and outfielder Braden Bishop round out the Mariners’ top five prospects.

So far in Carlson’s professional career he’s pitched three innings in two appearances with the Arizona Rookie League last season before being shut down with a sore elbow.

Carlson was committed to the University of Florida before signing with the Mariners on a $2 million bonus and he was considered by some in the industry as one of the best prospects to ever come out of Minnesota, which includes the Twins’ Joe Mauer.

Carlson threw a sinking fastball that touched 96-mph in the AZL and consistently pitched between 91-95 mph with a mid-80s slider. Baseball America also lists Carlson as possessing the best changeup in the Mariners’ organization among their top tools list.

He was ranked as the No. 15 prospect in the 2017 draft class at the time by ESPN’s Keith Law.

Other pitchers in the Mariners’ top 10 organizational rankings include right-hander Max Povse (six), right-hander Matt Festa (seven) and righty Art Warren (eight). Povse appeared in three games in relief for the Mariners last season and is currently starting for Double-A Arkansas, so is Festa and Warren.

The Mariners selected right-hander Logan Gilbert out of Stetson University, the same school that the Mets’ Jacob deGrom and Indians’ Corey Kluber are from, with their No. 14 overall pick in last month’s draft.