Alfonzo was listed in the starting lineup against the New York Mets, but his major league debut was pushed back when the game was postponed due to rain. It will be made up Saturday as part of a doubleheader beginning at 1:25 p.m.
Matt Cain, slated to pitch Friday night, will start the opener for San Francisco against Orlando Hernandez. Jamey Wright will go in the second game against New York's Tom Glavine, who had been scheduled to start Friday.
The 35-year-old Matheny was hit in the head several times by foul balls during a three-game series at Florida this week. He left Wednesday night's game in the third inning after a foul tip nailed him and was examined Thursday by a specialist in Pittsburgh.
"He's really got a mild concussion, which isn't bad, but he's had several of these," Giants trainer Stan Conte said. "The cumulative factor is something we're concerned about, but we don't think it's going to be a long time."
The four-time Gold Glove winner was placed on the DL retroactive to Thursday.
"He wholeheartedly agreed, which also tells you something," Conte said. "One thing about Mike Matheny, he's a very tough guy, but his brain is also made of the same stuff as everybody else."
Matheny is batting .231 with three homers and 18 RBI. He made one error in 862 chances last season, his first with San Francisco.
He has been on the DL twice before during his 13-year career, in 1998 with Milwaukee and in 2004 with St. Louis. Both were due to strained muscles in his side.
"We don't think this is going to be a long time -- but it's an important time, to make sure he fully recovers," Conte said.
The loss of Matheny leaves the Giants particularly short on catchers.
At Triple-A Fresno, Yamid Haad was suspended 50 games Wednesday after testing positive for a performance-enhancing substance. Todd Greene is the other backstop on the active roster, and he has started only nine games.
"It is a big blow," manager Felipe Alou said.
One sign: The jersey hanging in Alfonzo's locker had his name misspelled as "Alfonso."
No matter his name, the team's new catcher was being driven in a limousine from nearby Connecticut to New York. But because of the heavy rain, Alou cracked: "He would have been much better if he would have come by boat."
Even if the game had been played, the wet field might have kept Bonds out of the lineup. The 41-year-old slugger, who underwent three operations on his right knee last year, has had four straight days off after playing Monday in Florida.
He sat out Tuesday night's loss to the Marlins because of a sore back, and Alou rested him Wednesday without even checking on his condition. The Giants were off on Thursday.
Bonds hit his 715th homer Sunday in San Francisco to pass Babe Ruth and take over sole possession of second place on the career list. After playing chess with teammates in the clubhouse Friday, the seven-time NL MVP emerged to find a huge pack of reporters waiting in the hallway to ask him questions.
He said he's "very happy" about his accomplishment and grateful to all his peers around baseball who have offered him congratulations. He also reiterated he's still a long way from breaking Hank Aaron's career record of 755 homers.
"I want to win the World Series first, but if it comes up, I'm not going to stop playing," Bonds said. "Unless something happens, I get hurt, or injuries, or my son decides to change his mind and let me stay home."
This weekend marks the Giants' only visit to the Big Apple this year, and Bonds said he wasn't sure what to expect from New York fans. But he said he views negative reaction anywhere as "fun."
"Because if I was in their uniform, they'd be cheering," he said. "It's part of baseball. It's part of sports. It's always going to be like that. There's always one guy on the opposite team that's going to be the one that has to get booed.
"I don't take it personally."
Bonds said Roger Clemens' return to the mound with Houston is "good for the game" and he will be rooting for The Rocket along with many others. But the slugger doesn't see himself playing any partial seasons the way Clemens is preparing to.
"Roger took less money. I think he should have got more," Bonds said with a big laugh. "But I don't know, I'm not a pitcher. I'm an everyday player. So it's really hard to try to put yourself in that situation."
And lastly, Bonds was asked if he's bothered by all the talk about steroids.
"I think it bothers everybody. That's it," he said.
- The Giants hope to have slugging right fielder Moises Alou back early next week, perhaps as soon as Monday. He has been out since May 6 with a sprained right ankle, but Felipe Alou said his son probably doesn't need a rehab assignment to regain his timing because he has a compact swing and a simple approach to hitting.
- Mets CF Carlos Beltran was not in the lineup and would have been unavailable because of a bruised right knee. He fouled a ball off the knee Wednesday night against Arizona. Beltran wasn't sure if he would be able to play Saturday.