PHOENIX — Major League Baseball intends to push forward with the process that could lead to possible rule changes involving the strike zone, installation of pitch clocks and limits on trips to the pitcher's mound. While baseball Commissioner Rob Manfred expressed hope the ongoing process would lead to an agreement, he said clubs would reserve the right to act unilaterally, consistent with the rule-change provision of the sport's labour contract.

Union head Tony Clark said last weekend he did not foresee players agreeing to proposed changes for 2017. Under baseball's collective bargaining agreement, management can alter playing rules only with agreement from the union — unless it gives one year notice. With the one year of notice, management can make changes on its own.

"Unfortunately it now appears that there really won't be any meaningful change for the 2017 season due to a lack of co-operation from the MLBPA," Manfred said Tuesday during a news conference. "I've tried to be clear that our game is fundamentally sound, that it does not need to be fixed as some people have suggested, and I think last season was the kind of demonstration of the potential of our league to captivate the nation and of the game's unique place in American culture."

Yet, he also added: "I believe it's a mistake to stick our head in the sand and ignore the fact that our game has changed and continues to change."

Manfred said while he prefers an agreement, "I'm also not willing to walk away." He said he will send a letter to the union in the coming days and plans to continue dialogue with Clark and others in hopes of reaching agreement.

Clark met with Cactus League teams last week, five at a time over Thursday, Friday and Saturday, before departing Monday for Florida to visit each Grapefruit League club — and proposed rules changes were a topic.

"I have great respect for the labour relations process, and I have a pretty good track record for getting things done with the MLBPA," Manfred said. "I have to admit, however, that I am disappointed that we could not even get the MLBPA to agree to modest rule changes like limits on trips to the mound that have little effect on the competitive character of the game."

Clark saw talks differently.

"Unless your definition of 'co-operation' is blanket approval, I don't agree that we've failed to co-operate with the commissioner's office on these issues," he wrote in an email to The Associated Press. "Two years ago we negotiated pace of play protocols that had an immediate and positive impact. Last year we took a step backward in some ways, and this off-season we've been in regular contact with MLB and with our members to get a better handle on why that happened. I would be surprised if those discussions with MLB don't continue, notwithstanding today's comments about implementation. As I've said, fundamental changes to the game are going to be an uphill battle, but the lines of communication should remain open."

Clark added "my understanding is that MLB wants to continue with the replay changes (2-minute limit) and the no-pitch intentional walks and the pace of game warning/fine adjustments."

Manfred said he didn't want to share specifics of his priorities for alterations.

"There's a variety of changes that can be undertaken," Manfred said. "I'm committed to the idea that we have a set of proposals out there and we continue to discuss those proposals in private."

MLB has studied whether to restore the lower edge of the strike zone from just beneath the kneecap to its pre-1996 level — at the top of the kneecap. Management would like to install 20-second pitch clocks in an attempt to speed the pace of play — they have been used at Triple-A and Double-A for the past two seasons.

Players also have been against limiting mound meetings. The least controversial change appears to be allowing a team to call for an intentional walk without the pitcher having to throw pitches. In addition, MLB likely can alter some video review rules without the union's agreement— such as shortening the time a manager has to call for a review.

"Most of this stuff that they were talking about I don't think it would have been a major adjustment for us," Royals manager Ned Yost said.

Manfred said starting runners on second base in extra innings sounds unlikely to be implemented in the majors. The change will be experimented with during the World Baseball Classic and perhaps at some short-season Class A leagues. Manfred said it was a special-purpose rule "beneficial in developmental leagues."

Manfred also said Tuesday that a renovated Wrigley Field would be a great choice to host an All-Star Game and Las Vegas could be a "viable market for us."

"I don't think that the presence of legalized gambling in Las Vegas should necessarily disqualify that market as a potential major league city," Manfred said.

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AP Baseball Writer Ronald Blum and AP Sports Writer Bob Baum contributed to this report.