The New York Mets are going to find out what life is like without reigning National League Cy Young Award winner Jacob deGrom on Saturday afternoon. They won't know whether or not it will be a one-time thing until Monday.

Right-hander Chris Flexen will be promoted from Triple-A Syracuse in time to start in place of deGrom for the Mets on Saturday afternoon, when New York faces the host St. Louis Cardinals in the middle game of a three-game series.

DeGrom was due to get the assignment before the team announced he was headed to the injured list due to an issue with his right (pitching) elbow.

The Mets won the opener Friday night, when Wilson Ramos collected two RBIs in a 5-4 victory.

Flexen, who will be making his season debut with the Mets after going 1-1 with a 5.25 ERA in two starts at Syracuse, is scheduled to oppose Cardinals right-hander Miles Mikolas (1-1, 6.00 ERA).

The Mets will make room for Flexen on the active roster by placing deGrom on the IL, retroactive to Monday, due to a sore right elbow. Mets manager Mickey Callaway said Friday afternoon that deGrom felt "a little barking" in the elbow while playing catch Thursday.

Such news about an ace would be alarming for any team, but especially so for the Mets, who are built around their starting pitching and rewarded deGrom with a five-year contract extension worth $137.5 million last month. DeGrom opened the season with 13 scoreless innings over two starts but has allowed nine runs over nine innings in losing his past two starts.

General manager Brodie Van Wagenen attempted to quell concerns later Friday when he issued a statement noting deGrom's routine has been altered by a bout with strep throat -- deGrom was supposed to start Friday's opener but was pushed back due to the illness -- and that his right arm "felt significantly better following treatment with our health and performance staff today."

Van Wagenen added deGrom, who underwent Tommy John surgery in 2010 and had the ulnar nerve in his right elbow repositioned in September 2016, will visit with team doctors when the Mets return to New York on Monday. Callaway said after the game he hopes deGrom can come off the injured list next Friday, the first day he's eligible to do so, and start against the Milwaukee Brewers at Citi Field.

"He's in a good frame of mind right now," Callaway said following the game Friday. "I think the move we made was (done so for) no other (reason) than the earliest he'd be able to pitch is probably Wednesday, and then we have (an) off day, so we figured it'd end up being Friday. Going to see the doctor on Monday, so it just kind of made sense to go ahead and make this move."

Mikolas will look to rediscover the form that made him one of the biggest surprises in baseball last season, when he returned to the majors after three seasons in Japan and tied for the National League lead in wins with 18 while recording a 2.83 ERA over 200 2/3 innings.

The 30-year-old was rewarded in February with a four-year contract extension worth $68 million through 2023 and received the Opening Day start for the Cardinals. But Mikolas has lasted just five innings in three of his four starts, including his most recent outing last Sunday, when he allowed four runs (three earned) and didn't factor into the decision in St. Louis' 9-5 victory over the Cincinnati Reds.

Mikolas made his lone appearance against the Mets in 2012, when, as a member of the San Diego Padres, he tossed a scoreless inning of relief.

Flexen, who is 3-8 with an 8.45 ERA in 18 big-league games (10 starts), will be pitching in the majors for the first time since last July 8. He started for the Mets that day and took the loss after giving up five runs over three innings against the Tampa Bay Rays.

The 24-year-old California native has never faced the Cardinals.

--Field Level Media