Martinez will spend at least 10 days preparing to join the Mets after the season begins, Anthony DiComo of MLB.com reports.
It's unclear whether Martinez's preparation will occur in Triple-A games or at the Mets' spring training facility, but he won't be available to serve as New York's DH until after the second weekend of the season. Manager Carlos Mendoza said Saturday that once Martinez is ready to make his Mets debut, he will bat fourth in the lineup behind Pete Alonso, per Tim Healey of Newsday.