The MRI of his shoulder, which was the Mets' primary concern, was negative, but the one of his neck revealed the pinched nerve.
Sanchez threw in the bullpen prior to Sunday's game and said his neck was still too sore.
"There's no sense taking a chance," Mets manager Willie Randolph said.
The Mets hope Sanchez will be available Tuesday in Boston.
REPLAY: The home run ball has worked all season for the Mets, and it did again in Sunday's 7-4 victory over the Blue Jays.
The Mets got a homer from Jose Reyes to lead off the game, a three-run drive by Carlos Beltran in the third, and solo drive by Jose Valentin in the seventh to back Steve Trachsel.
Reyes had his fifth game with at least four hits as he extended his hitting streak to 13 games.
C Paul Lo Duca missed his second consecutive game Sunday with a bruised left thumb. Manager Willie Randolph said Lo Duca should be available Tuesday.
LHP Darren Oliver's strong 4 1/3-inning performance in relief of RHP Orlando Hernandez on Saturday could warrant him an opportunity to pitch in occasional situations against a left-handed hitter.
SS Jose Reyes extended his hitting streak to 13 games with a homer to lead off the game. It was his fifth career homer leading off a game, and his third this season. Reyes had at least four hits for the fifth time this season.
The Mets have hit at least one homer in 26 of their last 36 games. They got three Sunday, from SS Jose Reyes, CF Carlos Beltran and 2B Jose Valentin, to give them 79 in that span.
BY THE NUMBERS: 128 -- RBIs by 1B Carlos Delgado in interleague play through June 23, making him the all-time leader.