NEW YORK (AP) — Anthony Rizzo remained out of the Chicago Cubs' lineup Tuesday night against the New York Mets because of tightness in his back.

Ian Happ started in Rizzo's place at first base again in the opener of a critical three-game series. Chicago entered with a one-game lead over Philadelphia for the second NL wild card, while the Mets were two back. The Cubs were three games behind first-place St. Louis in the NL Central.

Cubs manager Joe Maddon and president of baseball operations Theo Epstein acknowledged Rizzo could miss the entire series. If he is able to return against the Mets, it would most likely be in Thursday's finale, Epstein said.

The team wants to be smart about the injury so Rizzo doesn't wind up missing an extended stretch.

"I know he's really frustrated by it," Epstein said. "We're hopeful it's just a couple days."

Rizzo left Saturday's game against Washington in the fifth inning and sat out Sunday, when the slumping Happ made his third career start at first base. Chicago had a day off Monday.

On a tear at the plate before getting hurt, Rizzo is batting .290 with 25 homers, 82 RBIs and a .928 OPS. The three-time All-Star is receiving treatment and feeling better, but backs can be "a cranky thing," Maddon said.

Rizzo, who turned 30 on Aug. 8, has a history of back trouble that caused him to miss time in May. The tightness this time is in a little different spot than usual.

"We're not overly concerned long term, but it seems like it's going to be a few days," Epstein said. "But these games are important, so you hate to lose him."

In other news, Epstein said the Cubs still expect utilityman Ben Zobrist back by the end of the month. Zobrist has been on the restricted list since May 8 while going through a divorce.

Zobrist is working on his timing and taking simulated at-bats this week at home in Tennessee against rehabbing or inactive pitchers. The team helped him set that up at his request, Epstein said.

The 38-year-old Zobrist played in a bunch of minor league games this month but no more are scheduled.

"He's in pretty good shape," Epstein said. "We still think utilized the right way, in the right matchups, not asking him to do too much, he can really help us."

ROSTER MOVE

Chicago placed pitcher Cole Hamels on the paternity list and recalled right-hander James Norwood from Triple-A Iowa. Hamels is still expected to make his next scheduled start Saturday.

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