Major League Baseball's postseason plan is nearly set, with the approval of the MLB Players Association all that's left standing between baseball and a bubble, sources told ESPN.

While questions about when and how families would enter the bubble remain unresolved, a neutral-site playoff format of some variety is expected to be finalized sometime next week, sources said.

In the March agreement between the parties, MLB was given authority to stage a postseason that mimics the bubbles that the NBA and NHL have used to shield their players and staffs from a COVID-19 outbreak. In order to modify protocols -- a key to a robust bubble -- the players must agree to changes.

Cursory bubble discussions in April fell apart when players expressed reservations about leaving their families for months at a time and the league balked at the logistical hurdles.

A bubble with a shorter lifespan is being negotiated between the league and union currently, sources said. Though the league does not need the players' approval to continue with the format, with so much at stake -- MLB could reap upward of $1 billion in postseason television revenue -- the willing participation of players is seen as a vital element to the sort of restrictions the league believes necessary.

Under the plan, the World Series would start Oct. 20 at Globe Life Field in Arlington, Texas, and would end no later than Oct. 28. It would culminate a month of playoff games that begin with the top four seeds in each league hosting all the games in a best-of-three wild-card series. The four American League series would run Sept. 29, 30 and Oct. 1, and the National League would play Sept. 30, Oct. 1 and Oct. 2.

The highest remaining seed in the NL would play its division series in Arlington while the next-highest seed would face its opponent at Houston's Minute Maid Park. The top seed from the AL would be the home team at San Diego's Petco Park, while the other series would be held at Los Angeles' Dodger Stadium. The AL Championship Series would take place in San Diego and the NLCS in Arlington, giving the NL's top seed -- likely the Los Angeles Dodgers -- a path to a stationary October.

Concerns from Dodgers players, which were first reported by The Athletic, underscore the chasm between the sides. Because MLB players have spent the season outside of a bubble -- and, in many cases, around their families -- the desire of some players to continue operating without the restrictions of a bubble are being voiced by the union, sources said.

Still, the prospect of a positive test waylaying the playoffs is palpable enough that MLB is insisting on the extra security a bubble notionally provides. A single positive coronavirus test can result in multiple postponements. In a strictly scheduled postseason, with TV network commitments, such a possibility could be devastating.

And with multiple positive tests in MLB this season being traced to family members, the league's position is simple: Either families go through a quarantine period, enter the bubble and live with players, or they can come to the host cities but remain socially distanced from players during the postseason.

While MLB hasn't suffered a significant outbreak since the St. Louis Cardinals' in July that wreaked havoc on their schedule, the fragility of the regular season -- let alone the postseason -- is clear. On Friday night, the San Francisco Giants postponed their game against the San Diego Padres following a positive test by someone in the organization. Saturday's game between the teams will be postponed as well, and if the teams follow precedent, they'll sit Sunday as well.

A bubble would theoretically help MLB weather any positive tests. The lack of travel days in a typical playoff series allows the league to bake in days to wait out potential positives. An outbreak, on the other hand, could prompt the league to force a team to play immediately using players from their alternate site, something it didn't do with the Cardinals or the other team that had a rash of COVID cases, the Miami Marlins.

The prospect of spending upward of a month isolated in hotels still is concerning enough to players that including family is a must. In any bubble scenario, the league would rent out entire hotels, allowing players and their families free rein on the property. They would not be allowed to leave the hotels except to attend games.

Concerns from the NBA and NHL bubbles about the tedium of life inside of them have spooked some baseball players, sources said. At the same time, they recognize the success of the other leagues' bubbles -- no one has tested positive in either -- and the potential harm of disrupting a playoff that teams see as vital to help deal with an altered financial landscape. There is already fear among some that the free agent market this winter could be slower than usual; a postseason interrupted by COVID cases could exacerbate that.

Striking a deal on when and how families enter the bubble is not the only hurdle. MLB also has asked for players to quarantine in hotels the last week of the regular season -- even teams playing at home -- so they don't need to undergo an intake period before the playoffs, sources said. For teams that make the World Series, that could amount to five weeks of bubble life.