Walker was replaced by Jose Reyes 10 minutes before the start of the Mets-Phillies game at Citizens Bank Park.
Although the Mets declined comment on a pending trade, a source said an announcement was expected later Saturday night.
Milwaukee's second-base contingent, which consists primarily of Jonathan Villar and Eric Sogard , ranks last in the league with a .672 OPS.
They traded closer Addison Reed to the Boston Red Sox and sent first baseman Lucas Duda to the Tampa Bay Rays before the July 31 non-waiver trade deadline, and they sent outfielder Jay Bruce to the Cleveland Indians for minor league pitcher Ryder Ryan on Wednesday.
Walker underwent season-ending back surgery last September and missed 36 games this year with a partially torn hamstring, but he told reporters this week that his health is not a concern.
- Report: Brewers to acquire Neil Walker from MetsYahoo Sports
- MLB Trade Rumors: Brewers reportedly close to adding Mets infielder Neil WalkerCBSSports.com
- Mets trade Neil Walker to Brewers, per reportNJ.com
- Mets close to finalizing a deal to send Neil Walker to the BrewersNew York Daily News
- Mets trade Neil Walker to BrewersNew York Post
- Mets trade Neil Walker to Brewers, source saysNewsday
- Reports: Mets Trade Second Baseman Neil Walker to BrewersSports Illustrated
- Milwaukee Brewers Acquire Neil Walker from New York MetsCall to the Pen
- Sources: Mets dealing veteran Neil Walker to the BrewersNorthJersey.com