Zack Wheeler went on the injured list Monday and the Giants swept a doubleheader, emphasizing how sensitive the starting pitching market is and how it can shift almost daily with every pain and gain between now and July 31.

The twists and turns obviously have not been good for the Mets. They can talk boldly that Wheeler will be back to make one or two starts before the deadline. But a shoulder injury is going to lower the return even if Wheeler makes it back. And Wheeler represented the item that would bring the greatest return among those whom the Mets are overtly shopping.

But the evolving market also has not favored the Yankees. Would the Mets have traded Wheeler to the other New York team? Probably not. But if Wheeler goes somewhere else — the Braves, for example — it would lessen the competition for other rotation pieces.

And what of those pieces? Not long ago, the Yankees at least could hope that the Nationals nosedived so badly that they would have to listen on Max Scherzer. On May 23, Washington was tied with Miami for the most losses in the National League. Since then, the Nats were an MLB-best 30-12 and had moved into the top wild-card seed.

The Rangers, expected to be sellers, have stayed in the wild-card race and have a stadium to open next year, dimming the possibility that Mike Minor will be dealt.

The Giants’ two wins over the Rockies on Monday gave them 10 victories in 12 games, driving them within three games of the second wild card despite being four games under .500. Rival executives still expect GM Farhan Zaidi to think big-picture and sell his most desirable pieces — namely Madison Bumgarner and a group of relievers led by closer Will Smith.

But there are forces pulling against that. The Giants won the World Series in 2010, 2012 and 2014, and at this time in those years, no one saw them as the team to beat. This is beloved manager Bruce Bochy’s last season, and there will be pressure to send him out with a contender if possible. The organization remains concerned about bleeding attendance and recognize a selloff is no aphrodisiac to fans.

“My take is that if [Zaidi] doesn’t get what he wants, he’ll hold his guys,” said a rival executive whose team is pursuing pitching. “Winning makes it easier to stick to his price.”

The Indians also continue to contend (an American League-best 23-10 since June 2), which could convince them to put an overwhelming price on Trevor Bauer and — if that is not met — just market him again in the offseason. But that would reduce Cleveland’s return. Rather than two playoff chases, an acquiring team would get just one from Bauer, who is a free agent after the 2020 season. Also, the Indians have leverage now. When Bauer’s salary next year climbs to $20 million-ish, suitors will know Cleveland pretty much must trade the righty.

But even if Bauer is available, the Yankees have more competition than expected. Could the rotation-needy Rangers be buyers rather than sellers? If Bauer is out of their price range, Bumgarner, Detroit’s Matthew Boyd, Arizona’s Robbie Ray and Toronto’s Marcus Stroman are options for the A’s (who already obtained Homer Bailey), Rays or suddenly surging Angels. A month ago, there was a belief the five AL playoff teams were pretty much set: Yankees, Rays, Red Sox, Twins and Astros. It is cloudier today. And the Twins and Astros were already in competition with the Yankees for starting pitching.

The volume of contenders seeking starters makes this a seller’s market in that area, yet no one is selling the kind of unquestioned ace for which an overpay is more palatable. For example, among those with at least 80 innings, Bumgarner is ranked 42nd in Fangraphs’ Wins Above Replacement. Ray is 44th. Sandwiched in between is Domingo German. Boyd, Bumgarner and Ray do not have as high groundball rates as the Yankees prefer in starters, and Ray’s 11.9 walk percentage is third-highest in the majors.

But Boyd and Ray are elite strikeout artists and Bumgarner has the glorious postseason pedigree. Bauer and Stroman come with questions about how they would be absorbed into a new clubhouse. Stroman is a groundball aficionado who lacks big strikeout numbers. Bauer, like Noah Syndergaard, has underperformed this season with the kind of high-end stuff that teams crave come October.

Which raises the question: In this seller’s market, should the Mets be aggressively selling Syndergaard? And would that just provide more unsatisfactory possibilities for the Yankees because the two New York clubs have not completed a trade involving major leaguers in 15 years?