The club will impose an innings cap on the 26-year-old right-hander.
DeGrom had been lined up to face the Houston Astros on Saturday at Citi Field. He has logged 140 1/3 innings in the majors this season, and 178 2/3 innings overall when his Triple-A work is included. That's already a jump of 31 innings from his 2013 total.
Collins said the Mets wanted to be particularly careful because deGrom's fastball velocity averaged a season-low 92.3 mph on Sunday against the Atlanta Braves.
"We explained the big picture," Collins said. "... One more start isn't going to vary any votes. One more start isn't going to show everybody that he belongs here. One more start could lead to some trouble. The big picture was to make sure when this season was over that those five [rotation] guys were going to be healthy. We think we've reached that point."
Said deGrom: "Obviously I wanted to make my last one, like I said in Atlanta. But they talked to me about it. The decision was made for me not to, and to end the year healthy. I respect that decision and I look forward to next year."
DeGrom's 2.63 ERA is the fourth best in franchise history among rookie pitchers who logged at least 140 innings, trailing only Jerry Koosman (2.08), Jon Matlack (2.32) and Dwight Gooden (2.60). Matlack (1972) and Gooden ('84) each won the NL Rookie of the Year Award. Koosman narrowly finished second to Johnny Bench in 1968.
Fellow Mets rookie Rafael Montero is expected to face the Astros instead Saturday.
DeGrom's 1.79 ERA since July 8 ranks second in the NL, trailing only Cy Young favorite and potential NL MVP Clayton Kershaw (1.75) of the Los Angeles Dodgers. During that stretch, deGrom went 28 innings without allowing an earned run -- the longest streak in the majors by a rookie since the San Francisco Giants' Matt Cain went 30 2/3 innings in 2006.
On Sept. 15 against the Marlins, deGrom matched a modern-day MLB record by striking out Miami's first eight batters.
In an underwhelming field, especially compared to the AL, deGrom's primary rookie of the year competition likely will come from Cincinnati Reds outfielder Billy Hamilton. The speedster is hitting .253 with six homers, 48 RBIs and 56 steals in 605 plate appearances, but he's been caught stealing 23 times and has a .295 on-base percentage. Hamilton's numbers particularly have sagged during the season's second half.
DeGrom would have the second fewest innings by a starting pitcher ever to win Rookie of the Year. Dave Righetti had 105 1/3 innings in 1981 with the New York Yankees.
The Mets' last rookie of the year winner was Gooden in 1984. He tweeted after deGrom won at Atlanta on Sunday to improve to 9-6:
- Dwight Gooden (@DocGooden16) September 22, 2014
DeGrom consistently during the second half maintained he was not thinking about the NL Rookie of the Year Award, but acknowledged his shutdown somewhat changes that mindset.
"That would be awesome," deGrom said. "Like I said, I try not to think about it too much. But now I'm thinking about it. That would be a great honor."
Closer Jenrry Mejia, who has pitched through a sports hernia during the second half, plans to undergo surgery on Oct. 2 in Philadelphia to repair the injury. Dr. Bill Meyers is due to perform Mejia's surgery.