NEW YORK -- Mets rookie third baseman Brett Baty will undergo surgery Thursday after an MRI revealed a UCL tear in his right thumb, the team announced Wednesday about 45 minutes before New York's game against the Los Angeles Dodgers.

The Mets said it typically takes five weeks to return from Baty's injury, which means he probably won't be healthy until the playoffs.

Baty, the 12th pick in the 2019 amateur draft, got hurt diving for a foul grounder last weekend.

The team placed Baty on the 10-day injured list retroactive to Aug. 29 and selected the contract of speedy outfielder Terrance Gore from Triple-A Syracuse.

New York can add more reinforcements Thursday, when major league rosters expand from 26 to 28 players.

A highly rated prospect, Baty was batting .184 with two homers and five RBIs in 11 games with the Mets during his first stint in the majors. With two third basemen injured, they called him up Aug. 17 after only six games at Syracuse following his promotion from Double-A Binghamton, and he homered in his first big league at-bat that night in Atlanta.

Hours before Wednesday's game, Mets manager Buck Showalter said Baty planned to take some swings to see if he could play with the injury or not.

Baty had been subbing at third for Luis Guillorme, sidelined with a groin strain, and Eduardo Escobar, who returned Saturday from an oblique injury.

Showalter said Guillorme could begin a rehab assignment on Sunday. Guillorme has been at Citi Field working out on the field and is expected to run the bases on Wednesday.

Guillorme is expected to platoon at third base with Escobar when he returns from the injured list.

In other Mets news, Tylor Megill is one step closer to returning to the New York rotation.

Megill will be starting a rehab assignment at Double-A Binghamton on Thursday night, according to Showalter.

The righty has been on the injured list since mid-June because of a right shoulder strain. While Megill began the season as a starter -- going 4-2 with a 5.02 ERA in 41⅓ innings -- he will return to the Mets as a reliever when he comes off the injured list.

The Associated Press contributed to this report.