McWilliams signed a minor-league contract with the Cubs on Monday, Ken Rosenthal of The Athletic reports.
The Padres outrighted McWilliams to Triple-A El Paso on Saturday.
McWilliams was claimed off waivers by the Padres on Saturday.
The Mets designated McWilliams for assignment Monday.
McWilliams returned from the COVID-19 injured list for Triple-A Syracuse on Friday.
McWilliams (undisclosed) was placed on the COVID-19 injured list, Tim Healey of Newsday reports.
McWilliams was optioned to Triple-A Syracuse on Tuesday.
McWilliams has impressed in the early stages of training camp and is battling for a spot in the Mets' bullpen, Tim Healey of Newsday reports.
McWilliams agreed to a one-year, major-league contract with the Mets on Friday.
McWilliams was added to the Rays' active roster Sunday, Marc Topkin of the Tampa Bay Times reports.