Niese received a cortisone injection in his left elbow Monday in New York to try to alleviate inflammation.
The Mets are not alarmed by the issue, but Niese needs more time to prepare for the season. He had missed time earlier in camp for shoulder weakness.
The team originally planned to have Niese pitch the March 31 opener against the Washington Nationals. Now, the plan is to have Niese pitch the sixth game of the season, April 6 against the Cincinnati Reds, also at Citi Field.
That is the day Niese would be allowed to be activated from the disabled list.
Teams are allowed to backdate DL trips nine days into spring training, as long as the player does not appear in a Grapefruit League game during that span.
Placing Niese on the DL will allow the Mets to carry an extra bench player for the first five games of the season, until the fifth starting pitcher is needed for the series finale against the Reds.
Niese should get two more tune-ups for the season in minor-league games: March 27 and April 1.
He is due to do work with a weighted ball on Thursday at the team's Port St. Lucie complex. Niese is due to resume throwing off a mound Monday.
The Mets have not named a replacement Opening Day starter. Dillon Gee, however, is currently lined up for the Opening Day start.