6:07pm: The Mets are hopeful that Rivera can avoid Tommy John surgery and will wait to see how his elbow responds to the PRP for awhile before making any type of determination, tweets MLB.com’s Anthony DiComo. It should be noted that the recovery time for position players that undergo Tommy John surgery is shorter than it is for pitchers, though the procedure would still leave Rivera on the shelf for several months and, depending on its timing, could potentially impact his availability for Spring Training.

5:10pm: The Mets activated second baseman Neil Walker from the 10-day disabled list today but were immediately hit with yet another dose of daunting injury news. New York announced that infielder T.J. Rivera is headed to the disabled list with a partial tear of the ulnar collateral ligament in his right elbow.

There’s no word yet on exactly how Rivera incurred the injury, but Mike Puma of the New York Post tweets that he’s already undergone a platelet-rich plasma injection. There’s been no suggestion yet that Rivera is pondering Tommy John surgery or a “primary repair” operation like the one Seth Maness and Mitch Harris underwent last year, though presumably, one or both of those treatments could become options, depending on the extent of the tear and how Rivera’s elbow responds to the PRP. James Wagner of the New York Times tweets that Rivera has been dealing with elbow soreness recently and wearing a tennis elbow wrap, but his discomfort has worsened in recent days.

Rivera, 28, has seen his name floated as a possible trade candidate — particularly when the Red Sox were on the hunt for infield help prior to the acquisition of Eduardo Nunez — and while he never seemed an especially likely candidate to move, this injury all but ensures that he will stay put. Since making his Major League debut with the Mets last season, Rivera has batted a healthy .304/.335/.445 with eight homers and 13 doubles in 344 trips to the plate. He’s played about 250 innings at both second base and third base for the Mets, while also logging 150 frames at first base and even nine in left field.

Unlike Rivera, the 31-year-old Walker is a much more definitive trade candidate. While he’s been out since mid-June with a partial tear in his hamstring, he was hitting a robust .270/.352/.468 with nine homers, 13 doubles and a pair of triples in 254 plate appearances at the time of his injury. There aren’t many teams looking for short-term help at second base right now — though Walker could conceivably help out at the infield corners as well — and Walker only has three games to display his health for interested teams.

However, Walker is also earning a fairly significant $17.2MM in 2017 after accepting a qualifying offer from the Mets last offseason. That sizable contract has about $6.1MM that remains to be paid, so it’s very possible that Walker will clear revocable trade waivers in the month of August. Assuming he clears waivers, the Mets would be free to trade Walker to any team through season’s end, though he’d need to be moved on or before Aug. 31 in order to be postseason-eligible with a new team.