The 38-year-old Giambi reported to Triple-A Colorado Springs, where he hit several home runs during batting practice Monday night. He said his troublesome right thigh was pain-free and that he was hoping for a Sept. 1 call-up to help the Rockies with their pennant push.
"I'm going to get a few at-bats down here and see how I feel. It's up to them when I get called up," Giambi said. "They're playing great baseball. I definitely don't want to go in there and disturb what they're doing."
Colorado went into Monday night's game against San Francisco with a three-game lead in the NL wild-card race.
"I was honored they called in the middle of a pennant race," said Giambi, who wasn't in the lineup against Reno on Monday night because he hadn't taken his physical. "They asked me if I wanted to go up and pinch hit and give [Todd Helton] a few days off. And I said I'd love to."
The Rockies could use another bat down the stretch along with more veteran leadership in the clubhouse.
"He's a veteran guy that understands this point and time of the season, that's been there and done that," Rockies manager Jim Tracy said. "To add him to your clubhouse with the character and makeup he brings, that's a tremendous plus for us."
Tracy has tried to give Helton regular rests this season so he doesn't have a recurrence of the back problems that plagued him last season, when he was limited to 83 games.
"As we go down the stretch, if Todd gets to where he absolutely needs a day, you have a guy who you can play there," Tracy said. "You don't have to completely tinker with the lineup and have guys hitting in all kinds of different spots."
Helton, who leads the Rockies with a .321 average, is happy with the signing.
"He's been there and done it," Helton said. "He's not going to be in awe of anything. When he walks up the plate you know he can hit a home run."
Giambi said he has no expectations beyond doing whatever he can to help the Rockies reach the playoffs for the second time in three years.
"There is no small role for a team in a pennant race," he said. "I've been in a lot of them in my career. The Rockies have a great ballclub. It seems like they have a great clubhouse. I know a lot of the guys and it would just be fun to be part of the ballclub -- even if it's giving high-fives."
Giambi was cut by Oakland earlier this month after hitting .193 with 11 home runs and 40 RBIs. He had been on the disabled list because of a strained right quadriceps before the A's released him, cutting short the struggling slugger's return to his first major league club.
A five-time All-Star, Giambi had returned to Oakland this season after seven seasons with the New York Yankees.
Although he has played all 1,933 games of his career for American League teams, Giambi has a .274 batting average with 44 home runs and 137 RBIs in 193 games against National League clubs in his 15-year career.
"Coors [Field] definitely won't be a bad situation to be in," Giambi said.
Tracy said if the Rockies did reach the playoffs, Giambi, who has a .289 average in 42 postseason games, could be on the 25-man roster for the postseason even if he didn't get much playing time in September.
"Having had to manage against him and knowing what he's capable of you can determine a lot quicker than if it was a novelty that you know nothing about," he said. "You know the history of this guy, so it's not like you need a long, long look to figure it out. You've got to find opportunities to get a glimpse and see where it's at and go from there."