Gywnn, who provided defensive versatility by playing at all three outfield positions this season, hit .163 (16 for 98).
With the recent addition of Grady Sizemore, there was less of a need for an extra outfielder.
"He had limited playing time as of late, but overall [he is] a terrific guy and teammate," Sandberg said.
Cliff Lee, Monday's starter, was activated from the 60-day disabled list. Infielder Reid Brignac and catcher Wil Nieves were activated from the 15-day disabled list.
Brignac (left-ankle sprain) was placed on the DL June 20. Nieves (right-quadriceps strain) was placed on the list June 24, retroactive to June 19.
Infielder Cesar Hernandez was optioned to triple-A Lehigh Valley. And catcher Koyie Hill was outrighted.
Both Nieves and Brignac said they are 100 percent healthy.
"My left hammy got a little tight, so it took me a little longer because of my hamstring, too," Nieves said. "But a little bit of rest and now I am ready to go."
Brignac said, "I felt great in my rehab games and was just eager to get back."
Catcher Carlos Ruiz, who went on the disabled list June 27 with a concussion, could return this week, according to Sandberg. Ruiz began playing Thursday in rehabilitation games for advanced-single-A Clearwater.
"We could be looking at the end of the week, possibly, something like that - if everything goes well," Sandberg said. "He needs some time to get his timing, see how he looks, how he feels, building his game strength, catching nine innings. He'll be monitored each game he plays."
Giant move at second
Even though Chase Utley must approve any trade because of his 10-and-5 rights (10 years in the majors, the last five with his current team), his name had been mentioned in connection with the Giants, who need help at second base.
However, the Giants signed second baseman Dan Uggla to a minor-league contract on Monday, three days after the Atlanta Braves released him. He will report to triple-A Fresno.
"We will get a chance to take a look at him, evaluate him," Giants manager Bruce Bochy said. "He will get a chance to go down and get his timing, get playing time."
Uggla hit .162 in 145 plate appearances this year.
"At some point, sure, we will have to make a decision," Bochy said. "I can't say he will be up here in the next few days; no, he needs some playing time."