The alternate training sites of 2020 infamy have returned to Major League Baseball.

Teams were informed Tuesday by MLB that the start of the Class AAA season will be delayed until the beginning of May and that they can set up alternate sites to keep players big league ready in the meantime, according to a memo sent to teams and multiple people familiar with the plans.

The Class AAA season had been scheduled to start on April 6. The newly remodeled Class AAA East is scheduled to begin May 4 and the Class AAA West on May 6.

Members of major league front offices had long been expecting the start of the Class AAA season to move back to early May, the same time the Class AA and A seasons were scheduled to start. In the memo circulated to teams Tuesday and obtained by The Washington Post, MLB explained the decision was made for “health and safety reasons,” including the hope that moving the season back a month will mean more minor leaguers will be able to be vaccinated before jetting off to affiliates.

Similarly, teams can implement more consistent testing and oversee covid-19 protocol adherence more closely at an alternate site than they can for their affiliates. So if they are in sudden need of a player, pulling them from an alternate site increases the likelihood that player will be healthy and ready for duty than if they are forced to use commercial travel options from sites around the country.

The memo did not outline details of the alternate-site rules, though multiple executives say their understanding, as informed by the protocols outlined in the Major League Operations Manual, is that they will be allowed 28 players on alternate-site rosters. The memo also did not delineate how long teams will be allowed to maintain those sites, though the assumption is that they will exist only until the start of the Class AAA season, at which point teams can pluck needed reinforcements from those clubs instead.

“I’m thinking and planning for this to roughly be about a 30-day experience. Then hopefully the minor leagues can get going in early May,” John Mozeliak, the Cardinals’ president of baseball operations, said Wednesday.

Most teams have not made their alternate sites official yet, though some may be forced to consider setting them up in Florida or Arizona because of unpredictable weather at facilities up north. Teams that play a large number of April games on the road would see little benefit from keeping prospects close to their major league park anyway and therefore could afford to keep their alternate sites in friendlier climates.

Current MLB protocol allows teams to carry a five-man taxi squad for road trips, so teams would have pretested players available to fill big league roster spots that open on road trips unexpectedly.

Multiple people familiar with the plans also believe teams will be allowed schedule exhibition games against other alternate site squads with MLB’s approval. While intrasquad games became the mind-numbing norm at many alternate sites in 2020, when the minor league season was canceled by the pandemic, players stashed there may be able to find fresher competition this time around.

“Obviously it’s not perfect,” Angels Manager Joe Maddon said. “But as long as they’re going to play, I’m good with it. As long as they’re going to get a full season of development.”

The makeup of the groups at those sites may also change. Many teams brought elite prospects to their alternate sites to ensure they played baseball somewhere in the absence of a minor league season, but prospects not yet ready for the big leagues can now spend spring training with their teammates and coaches from the Class A and AA levels instead.

“Ultimately, I think some of the younger players that could benefit from development, it might make sense to keep in [minor league] camp,” Mozeliak said.

The original schedule created a limited but real logistical conundrum: If the Class AAA season were to begin April 6, those players slated for Class AAA rosters would need to participate in some form of spring training in March. But major league clubs were limited to 75 players participating in big league camp at their facilities in March, with minor league spring training scheduled to begin when they vacated those facilities for the regular season.

In other words, each team would have to carry its entire Class AAA roster as part of a 75-player spring training pool or risk some players starting cold April 6. Most Class AAA candidates probably would be in camp already anyway, but with teams trying to give young prospects exposure, too, the numbers could get tight for some teams. The whole thing amounted to a headache for front-office staff trying to allocate talent to minor league rosters.

Now teams will be able to option players back and forth to the alternate sites as they did in 2020. If a player is optioned from the major league team to the alternate site, that counts as a use of one of that player’s option years, much like it would if he were assigned to Class AAA under normal circumstances.