Who Is Eligible to Join MLB Playoff Rosters?

Over the next week, 12 playoff teams will be looking to set their rosters for October baseball, trying to construct the best 26-man roster that can navigate the postseason waters and make it out on top as World Series champions.

When it comes to setting those rosters, there is often a great deal of confusion amongst fans on who is eligible to be added to a postseason roster, and who is ineligible. Can that top prospect crack the roster at the 11th hour after not playing in the big leagues all season?

How about that speedster who was added to the 28-man roster in September when rosters expanded and has played a huge role down the stretch to help his team make it to October?

While it may seem rather confusing, Major League Baseball’s rules on playoff rosters are actually a lot easier to understand than you would think. And that is because injury replacements allow teams to be very flexible with their rosters come playoff time.

Which Players Are NOT Eligible To Join a Playoff Roster?

If a player was not in his current team’s organization by August 31st, prior to the calendar flipping to September, they are not eligible to join a playoff roster.

So, if a player was claimed off waivers on September 1st, they are not eligible to join a playoff roster. Or if a player was signed off the streets after September 1st, again, they are not eligible to be on a playoff roster.

Other than that, EVERYONE else is eligible to be on a playoff roster.

As long as the player was in the organization prior to September 1st, they can be added to a playoff roster. So yes, even that 17-year-old who spent the 2025 season playing in the Dominican Summer League is technically eligible to join a playoff roster.

Walker Buehler is a great example from this season, as he was released by the Boston Red Sox on August 29th and signed with the Phillies on August 31st. Buehler signed a minor league contract, which brought him into the organization.

He later had his contract selected, and after three solid outings where he allowed just one run over 13 2/3 innings pitched, and considering his strong track record in the playoffs, Buehler is clearly going to make a postseason impact for Philly.

Who IS Eligible To Join an MLB Playoff Roster?

If we haven’t made it clear enough already, any player who was in his current team’s organization by August 31st is eligible to join their playoff roster. How they get added, though, is where a lot of the confusion comes into play.

If you go to MLB’s “Postseason Roster Rules & Eligibility” page, the first thing you will read is the following.

For the 2025 season, any player who was on the 40-man roster or 60-day injured list as of noon ET on Sept. 1 is eligible for the postseason.

Now, the way this reads, it is easy to assume that a player has to be on the 40-man roster prior to September 1st if they are going to make a playoff roster. Any player on the 60-day IL was on the 40-man roster previously, so this would suggest that players who have not cracked 40-man rosters yet are ineligible.

This is not the case due to the ability to add players as injury exemptions.

Injury Exemption Rule Explains All for Postseason Rosters

Here is where everyone gets lost, because what qualifies as an injury exemption is a bit ambiguous. This is how it reads in the rulebook:

A player who doesn’t meet said criteria for postseason eligibility can still be added to a team’s roster in the postseason via petition to the Commissioner’s Office if the player was in the organization on Aug. 31 and is replacing someone who is on the injured list and has served the minimum amount of time required for activation

When you read that a player can be added to the postseason via petition to the Commissioner’s Office, it makes you think these decisions are solely up to Rob Manfred’s discretion, and then you start to wonder what the criteria are that allow such a motion to be approved.

What we need to highlight is the final part of that rule, because it holds the key to understanding exactly how playoff rosters work.

We are focusing on the part that says “replacing someone who is on the injured list and has served the minimum amount of time required for activation.”

For a player to become an accepted injury replacement, they must replace someone who has been on the injured list for “the minimum amount of time required for activation.”

Take Walker Buehler, for example.

Buehler was not on the Phillies’ 40-man roster before noon on September 1st, but he was in the organization. Because he wasn’t on the 40, the Phillies need to add Buehler to their playoff roster as an injury replacement.

Look towards their injured list right now, you will find Zack Wheeler on the 60-day IL, and Jordan Romano and José Alvarado each on the 15-day IL.

Wheeler was added to the 60-day IL on August 31st. This means he has yet to spend 60 full days on the IL, or the minimum amount of time required for activation.

Jordan Romano, however, went on the 15-day IL on August 26th. This means he has spent the minimum amount of time required for activation, which allows the Phillies to make Buehler the injury replacement for Romano.

If you look through most teams’ rosters, there is bound to be an injured player or two who have been there for a long time. Especially with the prevalence of Tommy John surgery, most teams have at least one player sidelined on the 60-day IL for a major arm injury.

This is a loophole that teams can freely use, allowing them to be a bit more flexible with their roster decisions, without being forced to add every player they might want on their postseason roster to the 40-man before September 1st.

Again, if a player has spent the minimum amount of time required for activation on the IL, his team can add any player that was in the organization prior to August 31st as an injury replacement, and they WILL get approved via a petition to the Commissioner’s Office.

If a team has been remarkably healthy, they might not be able to take advantage of this injury replacement loophole, but from our quick search, looking at the 2025 playoff teams, each one has multiple players on the IL who have served the minimum amount of time required for activation.

So, as your favorite team sets its playoff roster next week, if you are wondering who is eligible to be added or not, all you have to remember is this: If the player was in the organization prior to September, you’re golden.