Diaz (shoulder) said after his rehab appearance with High-A Brooklyn on Thursday that he will get one more rehab outing Sunday before being activated from the 15-day injured list on Wednesday or Thursday, SNY reports.
Baty will be recalled from Triple-A Syracuse to serve as the 27th man during this weekend's series in London versus the Phillies, Mike Puma of the New York Post reports.
Alvarez (thumb) will be behind the plate for Triple-A Syracuse on both Friday and Saturday before serving as the designated hitter Sunday, Will Sammon of The Athletic reports.
Severino (4-2) picked up the win in Wednesday's 9-1 rout of the Nationals, allowing one run on seven hits over eight innings. He struck out four without walking a batter.
Mets manager Carlos Mendoza said Marte was scratched from the lineup prior to Wednesday's game in Washington due to a right knee issue, Mike Puma of the New York Post reports.
Peterson (1-0) picked up the win Tuesday, giving up two runs on five hits and two walks over 6.2 innings in a 6-3 victory over the Nationals. He struck out two.
Houser gave up two hits and two walks over 2.1 scoreless relief innings Monday to record his first hold of the season in Monday's win over the Nationals. He failed to strike out a batter.
Diekman pitched two-thirds of an inning and picked up the save in Monday's 8-7 victory over Washington. He struck out one and did not allow a baserunner.