ST. LOUIS - Michael Cuddyer could have started Friday night against the Cardinals.

Even though the Mets outfielder's bothersome left knee hadn't improved much even with the All-Star break, it would have been good enough to play on by baseball standards.

Even manager Terry Collins acknowledged as much.

Yet as the Mets began the second half of the season Friday night, the banged-up and struggling Cuddyer was reduced to spectator as a healthy scratch. Kirk Nieuwenhuis started instead.

The shift comes at a time when the Mets are exploring the possibility of adding an outfielder before the July 31 trade deadline.

"I've said it since Day One: I want to win," said Cuddyer, whose average dipped to .244 with seven homers and 29 RBIs in the first half. "That's the issue to me. Whatever Skip feels like is the best lineup is to help us win, that's what I'm on board for."

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Collins insisted that leftfield hasn't become a platoon, with the lefty-swinging Nieuwenhuis splitting time with the righthanded-hitting Cuddyer.

But Collins conceded that he will be consulting matchups to determine playing time, an indication perhaps that Cuddyer's could be reduced going forward.

Nieuwenhuis was hitting just .146, though he ended the first half with a three-homer barrage last Sunday.

"He deserves to be back out there after that game the other day, so we've got him out there tonight," Collins said. "Hopefully, he keeps hitting them out."

The Mets signed the 36-year-old Cuddyer to a two-year, $21-million contract in the offseason, a deal that also required the team to forfeit its first-round draft pick as compensation.

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In Cuddyer, the Mets saw another solid bat to plug into what they envisioned as a deep lineup, with production flowing from top to bottom. Instead, long-term injuries to David Wright and Travis d'Arnaud have gutted the lineup of its depth. And while Cuddyer has mostly stayed in the lineup, he has yet to find his stride at the plate, which has only amplified the offensive futility as a whole.

It's unclear how the Mets intend to address an outfield that has combined for a .666 OPS, tied with the Phillies for second worst in the National League.

Michael Conforto, the Mets' first-round draft pick (10th overall) in 2014, continues to sting the ball at Double-A Binghamton (.310/.390/.490). Though his relative lack of experience (145 at-bats in Double-A) has given the organization some pause about a promotion, the club has at least discussed the possibility. And team officials aren't philosophically opposed to fast-tracking Conforto.

The trade market also offers potential upgrades, and the Mets have been exploring those possibilities.

Justin Upton of the Padres, Carlos Gomez of the Brewers and Jay Bruce of the Reds represent some of the top-tier outfielders that could be available. But that trio could command bigger prospect returns, and the Mets have shown little appetitive for those kinds of deals. All three are viewed as long shots.

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But other options such as Will Venable of the Padres and Gerardo Parra of the Brewers would represent potential upgrades at a lesser price. Both could easily wind up on the Mets' radar.

A versatile outfielder could help the Mets hedge against Cuddyer's knee injury and also a banged-up Juan Lagares, who has endured a downturn both in the field and at the plate.