PHILADELPHIA -- Nobody really knows what Zack Wheeler will have Saturday night in Game 6 of the World Series.

Maybe even he doesn’t know.

But the Phillies hope it’s enough, because they need Wheeler to save their season after they lost Thursday night to the Astros, 3-2, in Game 5 of the World Series at Citizens Bank Park. Houston leads the best-of-seven series, 3-2, with Games 6 and 7 this weekend at Minute Maid Park. Only eight teams in baseball history have won a best-of-seven World Series by winning Games 6 and (possibly) 7 on the road.

Wheeler is one of baseball’s best pitchers, so there is almost nobody better to help them to try to become the ninth. But Wheeler also struggled in Game 2, when he experienced a notable drop in velocity. He is not injured, but he said he is experiencing arm fatigue.

“It’s the end of the season,” Wheeler told reporters on Thursday. “Everything is barking, you know what I mean?”

Wheeler threw a light bullpen session Thursday afternoon. He said it went well. But the arm is enough of a concern that the Phillies kept him as their Game 6 starter. They could have moved him to Game 5, like the Astros did with Justin Verlander, after rain postponed Game 3 on Monday. But Phillies manager Rob Thomson said Wheeler needed the extra rest.

Wheeler’s fastball velocity dropped from an average of 97 mph in his first four postseason starts to 95.2 mph in Game 2 at Minute Maid Park, where he allowed five runs (four earned) in five innings.

His fastball averaged 95.8 mph in the regular season.

Wheeler threw his four-seam fastball only 21.7 percent of the time in Game 2, which was the eighth-lowest mark of his 200 career starts, including the postseason. It was his lowest rate since Aug. 13, 2019.

Maybe that sixth day of rest will help.

“Time will tell,” Wheeler said.

Wheeler missed a month late in the season because of tendinitis in his right forearm. The Phillies have been careful with him since he returned. He has not thrown more than 96 pitches in any start, including the postseason.

Thomson said the Phillies might have ramped him up too quick.

“I think that took its toll on him a little bit, and I think that's why you're seeing now the velocity go down a little bit,” Thomson said.

Wheeler was asked if Thursday’s bullpen session felt better than the one he threw before Game 2.

“Why are you asking me all these questions?” Wheeler said.

It was a tongue-in-cheek response. The questions were asked because Game 6 will be one of the most important games in Phillies history. If the Phillies win Game 6, they will force a decisive Game 7.

And Wheeler at 98 mph is a different look than Wheeler at 95, although he pitched with success this season at that velocity.

“Zack's a competitor,” Phillies catcher J.T. Realmuto said. “Even in his starts this season, when his velo hasn't necessarily been as high as it always is, he always competes for us. He's got the stuff to get the job done. Whether his velo is at 98 or not, as long as he's got his command and then he's able to attack the strike zone and work ahead of hitters, I'm not too worried about the velo.”

It's anybody’s guess what it will be.

“I don’t know what it’s going to be when I go out there,” Wheeler said.