One home run shy of the milestone, Sheffield reached a contract agreement with New York on Friday, three days after he was released by the Detroit Tigers in a surprising move.
The deal is contingent on Shef-field passing a physical Saturday, Mets general manager Omar Minaya said.
The 40-year-old slugger, who played for the Yankees from 2004-06, gives the Mets a right-handed power bat, something they needed to help balance the lineup.
New York was already set at the corner outfield spots with Ryan Church in right and Daniel Murphy in left.
MARINERS: Ichiro Suzuki is being treated for a bleeding ulcer and was placed on the 15-day disabled list, sending Seattle into Opening Day minus one of baseball's best players.
The Mariners said the ulcer is no longer bleeding, but doctors have restricted the 35-year-old outfielder's activity.
Suzuki played for Japan in the World Baseball Classic. He complained of severe fatigue and missed Seattle's final three spring training games in Arizona, and was diagnosed with the ulcer after seeing doctors Thursday.
MARLINS: All-Star second baseman Dan Uggla was scratched from the starting lineup against Toronto because of tightness in his left calf.
The team described the move as "precautionary." Andy Gonzalez started at second base.
Uggla is batting .209 (14-for-67) with five home runs this spring.
ROYALS : Outrighted first baseman Ryan Shealy to Triple-A Omaha, trimming their roster to 30.
Shealy, who remained with the Royals for Friday night's exhibition game against the Texas Rangers, hit .262 with four homers and nine RBI in 23 spring training games before he was outrighted.