Diamondbacks reinstate Blake Walston from 60-day IL as September roster expands

What happened

The Arizona Diamondbacks announced the reinstatement of left-hander Blake Walston from the 60-day injured list, effective as active rosters expanded from 26 to 28 players on September 1. Outfielder Lourdes Gurriel Jr. was also reinstated, from the 10-day injured list, as the club's second addition on the same day. To create a 40-man roster spot for Walston, right-hander Ryan Thompson was transferred to the 60-day IL, per the club's announcement.

Why it matters

Walston's return is the kind of story that earns its own paragraph. He debuted with Arizona in 2024, making seven appearances and allowing nine earned runs across 18 1/3 innings. Then, in March of 2025, he underwent Tommy John surgery — the procedure that has a way of turning a promising young arm into a calendar-watching exercise for an entire organization. He spent all of last year on the injured list and the majority of this season there as well, meaning the Diamondbacks are only now getting their first real look at what he can do on a major-league mound since that debut.

The timing is deliberate, if modest in scope. September's roster expansion — from 26 to 28 players under current league rules — gave Arizona the structural room to bring Walston back without displacing anyone already contributing. The 40-man arithmetic required moving Thompson to the 60-day IL, which removes a player from the active 40-man count and opened the necessary slot.

The numbers

Walston is 25 years old, per MLB Trade Rumors. His entire major-league sample remains those seven appearances from 2024: nine earned runs across 18 1/3 innings. That is the full ledger. There is no 2025 line to reference, and his 2026 work has come exclusively on a rehab assignment that, per MLB Trade Rumors, has lasted almost a month. During that stretch he has been limited to appearances of one to two innings at a time — workloads that reflect the careful management typical of a pitcher returning from Tommy John surgery rather than any indication of what his ceiling might look like.

Arizona sits at 74-68 (.521) on the season, third in the NL West and 10.5 games back of the division lead. In the Wild Card picture the club ranks fourth, sitting 0.5 games relative to the cut line — close enough that every bullpen arm added in September carries at least some operational weight. The Diamondbacks enter this stretch on a one-game losing streak.

Where the club stands

### Is Arizona still in the Wild Card race?

At 74-68 and 0.5 games relative to the Wild Card cut line, the Diamondbacks are not comfortable, but they are not eliminated either. The margin is thin enough that the next several series will matter considerably.

The upcoming schedule does not offer much in the way of soft landings. Arizona hosts the Philadelphia Phillies at Chase Field on Tuesday, September 1, with Eduardo Rodriguez projected against Jesús Luzardo, and again on Wednesday, September 2, with Taylor Clarke lined up opposite Andrew Painter. The club then travels to Houston for a Friday, September 4 matchup at Daikin Park, where Merrill Kelly is projected to face Cristian Javier. The Phillies and Astros are not the kind of opponents that allow a bullpen to ease a returning arm back into the rhythm of things gently.

That context makes the shape of Walston's role worth watching. He is joining a bullpen that will be asked to navigate high-leverage situations against playoff-caliber lineups over the next several weeks. Whether he is ready for that, and in what capacity, is still an open question.

What we don't know yet

The most honest thing to say about Walston right now is that his role is genuinely unsettled. MLB Trade Rumors notes that he was largely a starter throughout his minor-league career, and the report raises the possibility that Arizona could look into stretching him out again at some point. For now, though, the expectation per MLB Trade Rumors is that he will work out of the bullpen — consistent with the one-to-two-inning appearances he has been making on his rehab assignment.

What that bullpen role looks like in practice — whether he pitches in low-leverage situations while the club monitors his workload, or whether he is trusted in tighter spots — has not been reported. The rehab assignment workload suggests the Diamondbacks have been cautious, which is entirely reasonable given the nature of his recovery, but it also means there is limited recent evidence to project from.

Ryan Thompson's transfer to the 60-day IL is reported as a roster-mechanics move to open the 40-man spot. No details about Thompson's status beyond that transaction have been reported.

What to watch

The immediate question is how quickly Walston is used and in what game situations. A pitcher returning from Tommy John surgery after missing essentially a full season and most of another is not typically handed a high-leverage role on arrival, but September rosters and playoff races have a way of accelerating timelines. Watch whether his appearances remain in the one-to-two-inning range that characterized his rehab work, or whether Arizona begins extending him.

The broader question — whether the club eventually tries him as a starter again — is one MLB Trade Rumors flags as a possibility but frames as a future consideration, not an immediate plan. For a 25-year-old left-hander with a minor-league pedigree as a starter, that conversation is probably not going away. It just is not today's conversation.

For now, Walston is back on a major-league roster for the first time since 2024, the Diamondbacks are half a game from the Wild Card cut line, and the Phillies are coming to Chase Field. The desk will be watching.