NEW YORK -- Steven Matz's back injury could prevent the rookie from starting for the New York Mets against the Los Angeles Dodgers in the NL Division Series.

New York said Matz woke Tuesday with a sore back. His start was pushed back at first by a day to Thursday and then he was scratched. Now the Mets are not counting on him to pitch this weekend against Washington in their final regular-season series.

''The concern level has certainly gone up. It hasn't seemed to get better,'' general manager Sandy Alderson said after Friday night's game was postponed by rain. ''I probably downplayed it a little too much at the outset based on hope rather than on information. But the fact that it hasn't responded particularly well is concern, but that doesn't mean it won't respond quickly over the next few days. These things are sort of hard to predict.''

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Having clinched the NL East title last weekend for their first postseason berth since 2006, the Mets are trying to finish ahead of the Dodgers for home-field advantage. Los Angeles (90-70) moved ahead of New York (89-70) by winning Friday night; the Mets hold the tiebreaker because they won the season series.

The rainout was to be made up as part of a day-night doubleheader Saturday, and the regular season is scheduled to end Sunday - which could be Matt Williams' final game as Nationals manager. Williams did not speak with the media after the postponement.

A 24-year-old left-hander, Matz made his big league debut in June and is 4-0 with a 2.27 ERA. He did not pitch for the Mets between July 5 and Sept. 6 because of a partial muscle tear on his left side. He has not appeared in a game since Sept. 24.

''Right now, I don't see how he's going to be ready to pitch this weekend,'' Mets manager Terry Collins said. ''Then we've got to get him to the Instructional League and get him some work.''

Collins will not be evaluating Matz's results in the Instructional League but rather how the pitcher feels.

''There's going to be six people there. It's going to be hot. So nothing dictates, except the workload,'' the manager said. ''And if he goes down and gets through that and comes out OK, I'd probably have to say there's a good shot he'll be on.''

Matt Harvey, NL Rookie of the Year Jacob deGrom and rookie Noah Syndergaard figure to be in the rotation against the Dodgers, and 42-year-old Bartolo Colon would be Matz's replacement. New York won't have to submit its Division Series roster until the morning of the opener on Oct. 9.

''If we decide that Steven is not in the rotation for whatever reason,'' Alderson said, ''he'll be considered for bullpen and either be put in it or not based on probably a whole different set of criteria.''

With rain forecast throughout the weekend, there is a chance home-field advantage could be decided with the Mets playing less than the full 162 games.

''We don't have clarity about that,'' Alderson said.

APPEAL

Mets reliever Hansel Robles is appealing the three-game suspension assessed by Major League Baseball for throwing near the head of Philadelphia's Cameron Rupp on Wednesday, delaying the start of any penalty.

TRAINER'S ROOM

Mets: Center fielder Yoenis Cespedes was in the posted lineup Friday, two days after two fingers in his left hand were bruised when hit by Justin De Fratus' pitch at Philadelphia. ... Infielder Juan Uribe, who hasn't played since Sept. 25 because of a chest cartilage injury, ''is not much better,'' according to Collins and Alderson. ... Infielder Wilmer Flores has strep throat.

WHAT'S NEXT

Noah Syndergaard (9-7) starts the 1:10 p.m. game for the Mets, and Gio Gonzalez (11-8) for Washington. Matt Harvey (13-7) goes for New York in the night game and Max Scherzer (13-12) for the Nationals.