WEST PALM BEACH, Fla. -- Carter Kieboom was almost at the end of his pregame fielding drills on Friday afternoon when, suddenly, something didn’t feel quite right in his throwing elbow. The discomfort was perplexing -- Kieboom had warmed up beforehand, and he hadn’t had any previous right elbow injuries. He hit in the cage in an attempt to loosen up, which provided temporary relief from the tightness, but as the 6:05 p.m. first pitch neared, he knew he could not make his scheduled start.

The following morning, Kieboom underwent an MRI and received disappointing results: a right forearm flexor mass/ulnar collateral ligament strain. He was placed on the 60-day IL on Monday.

The Nationals are planning on being without Kieboom for at least six weeks, after which Kieboom will likely require a rehab assignment before rejoining the club. It’s a disappointing development for the club’s former top prospect, and throws Washington’s current third base situation into flux. Maikel Franco profiles as the Opening Day starter now, unless the Nats make an additional move.

“It’s probably about six weeks of rehab and then getting him back to playing speed," said manager Dave Martinez. "We’ll work him in, but until we actually get him in a game will be the seventh week.” 

“I’m kind of shocked, I guess,” Kieboom said Sunday morning. “It was really out of nowhere. It really surprised me. There were no signs leading to it. Nothing alarming.”

Kieboom entered camp prepared to vie for the starting job at third base in his fourth Major League season. The 24-year-old made 59 starts there in 2021 (hitting .207 with a .958 fielding percentage), while also spending time developing with the Triple-A Red Wings. Kieboom arrived in Florida in February to face live pitchers and take ground balls, working out six days a week (pain-free) with the goal of earning the everyday role.

“[I worked on improving] really everything -- hitting, body, fielding,” Kieboom said. “I wanted to run better this year, so I lost some weight in the offseason. I just changed everything and how I was doing things. So it’s kind of a bummer.”

Entering camp, the competition for the hot corner was expected to be between Kieboom and eight-year veteran Franco , who signed a Minor League deal in December. Last season, Franco batted .210 with a .967 fielding percentage in 97 starts at third for the Orioles.

Franco, who also is an option to back up Josh Bell at first base, is looking to improve his patience at the plate, connect for more line drives and eliminate ground balls to shortstop and third.

“At the end of the day, it’s about going out there every single day and doing everything I can do to help my team to win and try to get better,” Franco, 29, said on Saturday. “My goal this year is to try to be healthy and ready to go.”

While Kieboom is sidelined, infielders Ehire Adrianza (685 1/3 career innings, .977 fielding percentage) and Richard Ureña (53 innings, .938 fielding percentage) also will get opportunities at third in Spring Training action.

“We’ll see how this plays out,” Martinez said when asked if the Nationals could consider outside options. “I know with such a short time, I’ve always said, [general manager] Mike [Rizzo], he’s going to look to see if he can make our team better.

“My focus is on the guys that we have in camp, and we’re going to try to get them ready.”