PHILADELPHIA -- Nationals ace Max Scherzer will not make his second-half debut Sunday as originally scheduled due to lingering back tightness that also prevented him from pitching in Tuesday's MLB All-Star Game.

The three-time Cy Young Award winner first felt some discomfort after his June 30 start against the Tigers, but his back responded well enough to pitch Saturday against the Royals. It wasn't until after that outing -- in which he struck out 11 over seven scoreless innings -- that it tightened up again.

Scherzer underwent an MRI on Wednesday, which came back clean.

"We anticipated for it to kind of loosen up over the All-Star break, and maybe even play catch Tuesday at the game," Scherzer said. "But it was just still tight. Just wasn't free enough for me to play catch. When you start doing the math on the days, I need to throw a bullpen, it just wasn't going to happen before Sunday."

Scherzer played catch on flat ground from approximately 75 feet Friday prior to the club's 4-0 win over the Phillies, and came out of that session without any issues. Manager Dave Martinez said it remains unclear when Scherzer will make his next start, while adding that Anibal Sanchez will start in his place Sunday.

The Nationals have an off-day Monday, before a brief two-game series against the Orioles. That will be followed by a four-game set in Atlanta against the division-leading Braves to wrap up a nine-game road trip.

"Tuesday's realistic. That's what we're hoping for," Scherzer said of his next possible start date. "This is not a major thing. We know exactly what this is, we know it's muscular. The pause for concern is that we tried to get it going for the Kansas City start, and it just wasn't able to recover from the Kansas City start. Now you got to go on a little different protocol to make sure I'm 100 percent right before I step on the mound again."

The back issue comes in the midst of one of the most dominant stretches of Scherzer's career. He is 7-0 with a 0.84 ERA over his last nine starts, while striking out 94 batters and walking just nine over 64 innings.

"He went out today and threw, and he felt a lot better," Martinez said prior to Friday’s game. "It’s a decision that myself, [general manager] Mike [Rizzo] and our training staff came up with -- just to push him back. You know Max, he always feels like he’s ready to go, but we need to do the smart thing here."

Rendon ready to go

It wasn't all bad news to start the second half for the Nationals, as Anthony Rendon -- the club's other All-Star -- made his 56th consecutive start at third base in Friday's series opener.

Rendon, who also missed Tuesday's All-Star Game, has been dealing with a nagging left hamstring injury and tight left quad since a three-game series in Cincinnati from May 31-June 2.

"He worked four straight days trying to get ready and he said he actually feels pretty good," Martinez said. "Kudos to him for staying back and getting stuff done and getting stuff right for the next run."

Though they had a pair of players selected, Tuesday marked the first time that a Nationals player did not appear in the Midsummer Classic since the club moved to D.C. in 2005.

"It stinks that those two guys couldn’t play in the All-Star Game, but they were smart about it," Martinez said. "Anthony has been pressing and pushing and playing with some bumps and bruises. He opted to do what’s right for himself and this organization and his teammates."

Venters lands on injured list

The Nationals placed southpaw Jonny Venters on the injured list, retroactive to July 8, with a left shoulder strain.

The veteran reliever said he felt some discomfort when he went to play catch the day after his July 5 outing against the Royals -- his third appearance with the Nationals.

"To be honest with you, that last game was the best I’ve felt in a long time," Venters said. "I know that the results weren’t there -- I lost us the game -- but I think I got six ground balls in that game. My arm felt good. Mechanically, I felt good. So it’s unfortunate to have the shoulder kind of flare up at that time, but hopefully it’ll feel better quick and I can get back out there."

The Nationals recalled Kyle McGowin from Double-A Harrisburg in a corresponding move, opting to let Kyle Barraclough continue working in the Minors.

"We want Barraclough to just hone in on everything," Martinez said. "McGowin’s been pitching good, but we just want Barraclough to gain some confidence, and get his mechanics right before we call him back up."