Rob Manfred explains MLB's decision to test a pitch clock in spring training and discusses the fractured relationship between the league and MLBPA. (1:31)

WEST PALM BEACH, Fla. -- Major League Baseball is unilaterally starting the use of pitch clocks for spring training games, while brushing off complaints from players about the slow free-agent market.

With the sport looking for ways to speed the pace of play, pitchers generally will have 20 seconds to deliver to the plate when teams play exhibition games in Arizona and Florida beginning this week. The intention is to get players and umpires accustomed to the clock in the event MLB makes the rule change for the upcoming regular season.

"We will start getting ready for the possibility that we're going to use the pitch clock on Opening Day,'' commissioner Rob Manfred said Sunday at spring training media day in Florida. "We have to get going.''

After the 2016 and 2017 seasons, players rebuffed management's proposal for a pitch clock. Owners have the right to implement one this year without consent, but Manfred has been reluctant to initiate on-field modifications without agreement from players and their union head, Tony Clark.

"We're still hopeful that we're going to make an agreement with Tony on pace-of-play initiatives,'' Manfred said. "I just think that whether it's by agreement or otherwise, the only prudent course for us at this point is to be in a position to proceed if in fact we have an agreement or decide to do it ... under our collectively bargained right to do that.''

MLB made a unilateral decision on clocks for the exhibition season.

"We will start getting ready for the possibility that we're going to use the pitch clock on Opening Day. We have to get going." Rob Manfred

"We were recently notified by the commissioner's office that the pitch clock will be tested in spring games,'' the players' association said in a statement. "This is not the result of an agreement with the players' association. Discussions regarding several on- and off-field issues remain ongoing.''

Clark said in a separate statement Monday that players have made a sincere attempt to engage with clubs on their proposals to improve pace of play.

"We have presented wide-ranging ideas that value substance over seconds and ensure the best players are on the field every day. We believe these substantive changes are imperative now -- not in 2022 or 2025, but in 2019."

Manfred said the rules involving the clock will be "phased in'' and won't start immediately with ball and strike calls. But there will be a "functional'' clock in Grapefruit League and Cactus League games.

Management's proposals have said a clock would not be used after foul balls. Pitch clocks have been used in the high minors since 2015.

With spring training underway and exhibitions scheduled to start Thursday, several players around the majors have taken issue with a second consecutive slow market for free agents. They question why more teams aren't trying to win.

"It would be nice to start with the facts on this topic. There has been no meaningful change in the distribution of winning percentages in Major League Baseball,'' Manfred said. "Our teams are trying. Every single one of them wants to win. It may look a little different to outsiders because the game has changed, the way that people think about the game, the way that people think about putting a winning team together has changed, but that doesn't mean they're not trying.''

Two of the game's biggest stars, Bryce Harper and Manny Machado, remain unsigned this offseason. Rob Carr/Getty Images

Two of the game's biggest stars, Bryce Harper and Manny Machado, remain unsigned -- along with closer Craig Kimbrel and dozens of other accomplished veterans.

"There are 11 players who had a WAR [wins above replacement] above one last year that are unsigned. I believe that just like last year, that market is going to clear. At some point here in the next few weeks, those players are going to get signed,'' Manfred said. "We negotiated a system that allows the market to operate and I have every confidence that for those players that I just described, that market is going to clear before we get to playing real games.''

The current economy for players is all part of the game, he insisted.

"I think it's important to remember that the Major League Baseball Players Association has always wanted a market-based system. And, markets change. Particularly when the institution around those markets change. We've had a lot of change in the game. People think about players differently. They analyze players differently. They negotiate differently. Agents negotiate differently,'' Manfred said. "I think there's lots and lots of offers out there, and it's a bilateral process. Players haven't accepted those offers yet. That's how a market works. So you know, we bargained for a market system, that market's out there operating, and I don't have any choice but to live with that right now.''

In a statement released Monday, Clark pushed back on Manfred's comments, calling them "unconstructive."

"As players report to spring training and see respected veterans and valued teammates on the sidelines, they are rightfully frustrated by a two-year attack on free agency," Clark said in a statement. "We're operating in an environment in which an increasing number of clubs appear to be making little effort to improve their rosters, compete for a championship or justify the price of a ticket."

Manfred said just because clubs don't spend big doesn't mean they aren't attempting to win. He pointed out that the Oakland Athletics and Tampa Bay Rays, two low-payroll clubs expected to struggle in 2018, both had excellent seasons.

The Athletics reached the playoffs with 97 wins, and the Rays won 90 games.

"I reject the notion that payroll is a good measure for how much a team is trying or how successful that team is going to be,'' Manfred explained.

That drew the ire of Houston Astros ace Justin Verlander, who tweeted:

Agreed... finally we're on the same page! Awesome! Removal of the luxury tax it is. https://t.co/Omy0SaXZ1z — Justin Verlander (@JustinVerlander) February 18, 2019

The Associated Press contributed to this report.