MILWAUKEE - When Mets manager Terry Collins ventured into the trainers' room on Sunday in Atlanta, he spotted trouble immediately. One day after hyperextending his left elbow in a home-plate collision, catcher Travis d'Arnaud still was experiencing discomfort.

Collins braced for the worst.

On Monday morning, it came in the form of an email from team trainer Ray Ramirez, the first step in a chain of events that sent d'Arnaud to the disabled list with what the team is calling a sprained left elbow.

"We're getting numb, I think," said Collins, who has managed through a season-long rash of injuries. "We're pretty much numb to the whole situation."

The injury once again robs a sputtering Mets offense of one of its few productive bats, which haunted them again Tuesday night in a 3-2 loss to the cellar-dwelling Brewers.

The Mets dropped their sixth straight despite a quality start from Jonathon Niese (two runs in six innings) and a homer from Curtis Granderson (his 10th).

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For the first time since April 12 -- the beginning of an 11-game winning streak -- the Mets (36-36) have tumbled back to the .500 mark.

The defeat, like many on this winless road trip, was hastened by a glaring defensive lapse. This time, leftfielder Michael Cuddyer committed the offense. It came in the seventh, when Adam Lind's double caromed off the side wall and through Cuddyer's legs.

The gaffe allowed Carlos Gomez to score from first and break a 2-2 tie.

The mistake typified the Mets' recent struggles, which have only been amplified by a lineup that has produced eight runs in the last six games.

It only got worse with the injury to d'Arnaud who was hitting .267/.313/.533 with two homers and seven RBIs in eight games since returning from the DL on June 10. He had been sidelined since April 20, first with a broken little finger on his right hand, and then by a bone bruise on his right wrist that slowed his rehab.

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His loss comes with the club's roster already stretched thin without third baseman David Wright and second baseman Daniel Murphy.

"He's a big part of our offense and a big part of our team," assistant general manager John Ricco said.

Now, they must turn toward a relatively inexperienced fill-in, Kevin Plawecki, to help bridge the gap until d'Arnaud's return.

The rookie Plawecki is hitting .231 with two homers and 14 RBIs, though he until recently had been battling sinus problems that caused dizziness.

As has been the case with other players, the Mets initially thought d'Arnaud's issue to be far less serious. Even d'Arnaud expressed relief when X-rays revealed no fracture after a throw forced him up the third-base line, directly into the path of an oncoming A.J. Pierzynski.

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But on Sunday, Collins sensed a major issue. On Monday, a team off day, d'Arnaud awoke with discomfort. He was sent for an MRI exam that prompted the team to send him to New York for a physical exam.

The Mets recalled Johnny Monell from Triple-A Las Vegas before they knew that d'Arnaud would require a DL stint.