Mets leftfielder Michael Cuddyer bobbles a ball hit for an...

Mets leftfielder Michael Cuddyer bobbles a ball hit for an RBI single by St. Louis Cardinals' Jason Heyward during the first inning of a baseball game Saturday, July 18, 2015 in St. Louis. Credit: AP / Jeff Roberson

The Mets had already been seeking an outfielder in the trade market. But their search could intensify if Michael Cuddyer's balky left knee doesn't respond well to what he called a last-ditch effort to manage the pain.

If it doesn't work, Cuddyer will likely land on the disabled list.

The 36-year-old veteran left in the eighth inning of Sunday's marathon 3-1 win over the Cardinals in 18 innings.

Once again, he felt pain stemming from the bone bruise in his left knee, which has plagued him since just before the All-Star break.

A stint on the disabled list would mark yet another disappointment during Cuddyer's rough first season with the Mets. He signed a two-year, $21-million deal in the offseason, which also cost the Mets a first-round draft pick in this year's draft.

But he has hit just .250 with eight homers and 30 RBIs.

Cuddyer's down season has only accentuated the lack of production from an outfield that features a languishing Juan Lagares and little help off the bench from Kirk Nieuwenhuis and John Mayberry Jr.

The Mets have already been linked to outfielders such as the Padres' Justin Upton, the Brewers' Carlos Gomez and the Reds' Jay Bruce. They also appear to be gravitating toward other choices such as Will Venable of the Padres and Gerardo Parra of the Brewers.

The Mets appear hesitant to deal top-flight starting pitching or some of their elite prospects such as Michael Conforto, who remains unlikely to be fast-tracked to the big leagues in the near future to help the Mets' ailing offense.

However, within the organization, the Mets believe they have enough prospect depth to pull a deal together.

That group includes the likes of Michael Fulmer and former first-rounders Brandon Nimmo and Gavin Cecchini.

Manager Terry Collins said Cuddyer informed him that he could no longer run after he advanced to second base on a wild pitch.

"It's just much of the same, really," said Cuddyer, whose status hinges on his ability to manage pain.

He has already had a cortisone injection, though that hasn't been enough to stem the symptoms. Collins made reference to another pain-relief measure the Mets will attempt Monday, though he refused to get into details.

"It's concerning," said Cuddyer, who described intensifying pain as the game went on. "We're trying different things to get through it, to get relief."