Nimmo was scratched from the Mets' lineup prior to Thursday's game against the Phillies due to a stomach illness, Mike Puma of the New York Post reports.
Diekman gave up an unearned run in the 11th inning Thursday, walking one and striking out one, to record his first save of the season in a 6-5 win over the Phillies.
Pirates director of sports medicine Todd Tomcyzk said Friday that Hayes (back) will resume baseball activities Monday, Andrew Destin of the Pittsburgh Post-Gazette reports.