Manager Dale Sveum said he remembered Gillespie from his days in Milwaukee when Gillespie, still in the minors at the time, spent a spring with the Brewers.
"Really sound, fundamental baseball guy," Sveum said. "He's obviously not gotten a whole lot of reps in the big leagues, but real nice minor league numbers."
Gillespie has played 53 games in the big leagues with the Giants and Arizona Diamondbacks, hitting .218/.277/.361 with three home runs.
Gillespie, 29, had an .863 OPS in parts of eight seasons in the minor leagues. Gillespie played college baseball at Oregon State and won a College World Series with Darwin Barney as his teammate.
"I think he's a good pick up for us," Barney said. "All-state shortstop kind of guy, good athlete. Right-handed bat that we kind of need right now. I'm excited to finally play with a teammate that I've played with in the past."
Sveum said Gillespie would join the team Sunday and would likely play against lefties. A corresponding move to make room for Gillespie on the roster will be announced Sunday.
Schierholtz sits: Nate Schierholtz was held out of Saturday's lineup and Sveum said he'd sit him Sunday as well. That would give Schierholtz six days off before the Cubs return to action Friday after the All-Star break.
"He's a little banged up," Sveum said. "Obviously I may have to play him in the outfield or something, but I'll try to stay away from him. Just banged up, struggling a little bit, so I just thought I'd give him a few extra days off."
Sveum didn't get into specifics as to what was ailing Schierholtz, saying that it was "just a little bit of a lot of body parts."
Schierholtz has struggled in his last 13 games, putting up a .140/.241/.180 line over that span. It's possible that getting his first shot of playing on a near-daily basis is starting to catch up to the right fielder. Schierholtz has played in 77 games this season and amassed 279 plate appearances.
Only 91 games into the season, it's a good bet that Schierholtz will surpass his previous career high of 362 plate appearances at some point in the near future.
Schierholtz has posted great numbers in his first year with the Cubs, slugging a career high .498 with 11 home runs while posting a strong .862 OPS against right-handed pitchers.
Rehab updates: Sveum said center fielder David DeJesus will go to Arizona on Monday and take batting practice. If he comes out of that session healthy, he'll likely play in some games in the Arizona League before starting a rehab assignment with one of the Cubs minor league affiliates, possibly as early as Friday.
DeJesus has been on the disabled list since June 15 because of a right shoulder sprain.
Pitcher Scott Baker is also on the mend as he makes his comeback from Tommy John surgery. Baker will pitch for the Kane County Cougars (the Cubs Low-A affiliate) at West Michigan on Sunday. Sveum said Baker will throw around 65 pitches and hopefully four innings.
Minor league outfielder Brett Jackson has been on the disabled list since June 22 and will head to Mesa to continue his rehab on his strained right calf. It's possible that Jackson, who has spent the entire season with the Triple-A Iowa Cubs, may head to Double-A Tennessee when he's ready to return to game action.