NEW YORK -- Mets manager Terry Collins was ejected from Tuesday's game against the Rockies in the fifth inning for arguing an overturned call on the basepaths.

Second-base umpire Lance Barksdale originally called Andres Torres safe at second base, after Rockies pitcher Jhoulys Chacin fired a pickoff throw and caught Torres straying too far off the bag. Chacin threw to shortstop Jonathan Herrera, who relayed to third baseman Jordan Pacheco as Torres was caught in a rundown and scurried back into second.

But Pacheco caught up to Torres as he neared the base, sliding with him and appearing to tag him on the right leg. After Barksdale initially called Torres safe, third-base umpire Fieldin Culbreth met with Barksdale to overrule the call.

That brought Collins out of the dugout in a rage. He argued with Culbreth, earned his ejection and then argued some more before retiring to the clubhouse.

Johan's MRI results to be revealed today

NEW YORK -- A day after insisting that Johan Santana has more to offer the Mets in 2012, the team deliberated over MRI results on Santana's ailing back. Santana underwent an MRI at the Hospital for Special Surgery in New York on Tuesday, and the Mets plan to announce the results on Wednesday.

All the while, they made a contingency plan in the event that Santana will not start on Thursday -- a development that would likely end his season. Should Santana not pitch, Collin McHugh will make his Major League debut in his place, with the Mets continuing to utilize a six-man rotation.

Santana is 6-9 with a 4.85 ERA in 21 starts, though that hardly tells the story of his summer. Pitching for the first time since undergoing anterior capsule surgery on his left shoulder in September 2010, the left-hander began the year 3-2 with a 2.38 ERA over his first 11 starts, striking out 68 batters in 68 innings and throwing the first no-hitter in Mets history on June 1 against the Cardinals.

But he threw 134 pitches in that start and has scuffled since, dropping seven of his last 10 decisions with an 8.27 ERA. An ankle injury pushed Santana to the DL in late July, and he has allowed 14 runs in 6 1/3 innings since returning. Over his last five starts, Santana has gone 0-5 with a 15.63 ERA.

Partly because of that, the Mets wanted Santana to continue pitching in order to finish his season on a high note, starting the lefty perhaps twice more before shutting him down for good. As recently as Monday, the Mets expected Santana to remain in the rotation until rosters expanded on Sept. 1. But Santana threw a bullpen session that afternoon, felt his back stiffen afterward and went for an MRI the following day.

If nothing else, that development has caused the Mets to rethink their plan.

"We're not going to wear him out," manager Terry Collins said.

To guard against the possibility that Santana will not pitch Thursday, the Mets plan to bring McHugh to Citi Field on Major League Baseball's taxi squad, allowing them to activate him in time for Thursday's start. McHugh, 25, is 2-2 with a 2.45 ERA, 52 strikeouts and 19 walks over his last nine starts for Buffalo, and will be on regular rest. Despite lacking the same prospect pedigree as Jenrry Mejia, who was also considered, McHugh turned heads by dominating for Double-A Binghamton over a 12-start stretch earlier this year. He will likely join the club in September regardless.

The Mets have already dismissed the option of reverting to a five-man rotation, preferring to continue giving Chris Young, Jon Niese and Matt Harvey regular breaks to dampen their workloads down the stretch.

With Hefner on paternity list, Mets recall Carson

NEW YORK -- The Mets placed right-hander Jeremy Hefner on the paternity list Tuesday, freeing him to fly home to Oklahoma for the birth of his second child. Hefner's wife, Sarah, is scheduled to give birth on Wednesday, giving Hefner plenty of time to return to New York in advance of Sunday's scheduled start against the Astros.

To replace Hefner in the interim, the Mets recalled lefty reliever Robert Carson from Triple-A Buffalo, where he posted a 1.72 ERA in 10 appearances. With Tim Byrdak out for the season, Carson could receive ample work once rosters expand in September, teaming with Josh Edgin as a second lefty in New York's bullpen.

Because of that, the Mets were glad to afford Carson a bit more big league experience in advance of his September assignment.

"I'd like to try to, if I can, have him face somebody," manager Terry Collins said. "The more times I run him out there, the better idea we'll have. I think obviously there's a pretty good chance he'll be here in September anyway, so it would be good to get him some more time on the mound."

Children can see Mets for free Thursday

NEW YORK -- Children 12 and under will have an opportunity to attend Thursday's Mets game for free, the team announced Tuesday.

For the Mets' 1:10 p.m. ET game against the Rockies, up to three children 12 and under will get free admission with the purchase of a regularly priced ticket. The Kids Go Free offer is available in person at the Citi Field box office, as well as at 718-507-TIXX. A similar offer is available on mets.com/KidsFree via the Family Four Pack, which includes four tickets for the price of two.

All tickets must be picked up at Citi Field the day of the game, with children present.