Matheny didn't feel well after trying to elevate his heart rate on Friday in San Diego, and the altitude in Denver likely contributed to his symptoms.
With each passing day, it's becoming clear that Matheny's concussion is more serious than anyone imagined. At this point, there is no guarantee he will play again this season.
"It's going to take the time it needs to take, regardless of how fast I want it to be," Matheny said on Monday. "I'll work out a little bit and it just responds badly to it."
Matheny wasn't sure when he would make another trip to Pittsburgh to consult with head trauma specialist Dr. Michael Collins. He will not receive medical clearance until his symptoms disappear completely.
Matheny hasn't played since he was struck by a foul tip May 31 at Florida, and now suspects he has sustained multiple concussions over his career.
MOISES READY FOR L.A.? Moises Alou took batting practice with the team and appears to be eyeing a return Thursday when the Giants open a four-game series at Dodger Stadium.
Alou spent most of his 40th birthday in a doctor's office in South Florida on Monday, receiving a second opinion on his lower back. The specialist confirmed the diagnosis of an inflamed facet joint and Alou said he felt better.
The Giants plan to option a pitcher to make roster space for Alou, likely Brian Wilson or Jonathan Sanchez.
JACK'S BACK: Jack Taschner didn't arrive in the clubhouse so much as he bounced into it.
The Giants recalled the high-energy left-hander from Triple-A Fresno and optioned infielder Kevin Frandsen, temporarily putting them at 13 pitchers.
Taschner began to turn things around in early May when special assistant Ron Perranoski advised him to scrap his curveball. He began throwing his slider and fastball for strikes and pitched well after replacing Merkin Valdez in the closer role.
"Was I antsy? Yes. Frustrated? No," Taschner said. "Of course I wanted to get back here, but everybody was throwing the ball really well. I understood the situation."
Frandsen was glum about his third demotion, especially because he was looking forward to his first series at Dodger Stadium. Frandsen started just one game after the club recalled him June 21, even though he was promised more playing time.
ONE-HOPPERS: Felipe Alou received a slew of congratulatory calls after winning his 1,000th game as a big league manager Monday night. Rockies skipper Clint Hurdle, who played for Alou in winter ball, sent over a bottle of wine. ... Valdez, a former top prospect, hasn't sorted out his command issues at Fresno, but Taschner said he is still blowing 98 mph fastballs. ... Colorado's Yorvit Torrealba admitted he was too hyped up for his first game against the Giants on Monday, and Noah Lowry exploited it by getting his former catcher way out in front of his changeup. "I know he can hit the fastball," Lowry said with a smile.