Nicknamed "Woody" for his resemblance to the Toy Story cowboy character, the 34-year-old Rueter's usual ebullience was missing when told of the decision.
The lefty had only pitched three times since July 4, including one disastrous relief stint July 29 at Milwaukee, then went on the disabled list with gout.
"I probably will be sad, but I don't know why they made me sit for 41 days and then put me on the DL, when they knew I didn't want to go on it last week," said Rueter, who had lobbied the past two weeks to give him a chance with another club.
"It could have been handled a bit better than what it was, considering I've pitched only three times -- not that I've been keeping track. I didn't know what to expect ... but everything is going to end sometime."
Rueter has had a two-season slide after achieving seven years of double-digit victories, falling to 9-12 and 4.73 ERA last year and struggling this season with a 2-7 record and a 5.95 ERA.
He hasn't won a game since May 13, a 4-2 decision at Houston.
Although Rueter isn't a loud man, he was admittedly miffed at the Giants dragging his season out when he desperately wanted out to go elsewhere as September approached.
"That's what I'm more mad about -- I've been telling them I want to pitch," said Rueter. "That's the most frustrating part for me. I've been fortunate to have been here for nine years and been able to play on great teams, but the competitor in me has wanted to pitch the last month and a half."
Still, it was a jolt to the club as Rueter packed his bags and prepared to fly to his home in rural Nashville, Ill., where his wife, Karla, and young daughters, Hope and Halle, reside.
His famous "Shed," has long been a haven for his teammates and pals, and Rueter indicated he'd still invite Giants to the recreational facility when they play at St. Louis this week.
General manager Brian Sabean was also saddened by the move.
"The business of baseball is unforgiving, but I can tell you I didn't sleep last night, so it wasn't easy," said Sabean, who joined the club in 1997, Rueter's first full year with San Francisco.
Sabean said he has tried to work a trade with the veteran but was stymied in conversations with other clubs, then said the gout protracted the problem.
"Now with him eligible today [to be activated], we had to make a move and thought it was more prudent to get his name out there by designating him for assignment," said the GM, noting he had thought a deal would happen this weekend.
Manager Felipe Alou, who first managed Rueter at Montreal in 1993, said it was indeed a doleful day, noting Rueter's eyes the past few weeks have betrayed the pitcher's emotions, despite the smiles.
"I've been sad the entire time -- he's a tremendous man," said Alou. "He came up to the big leagues when he was 22 or 23, and went through tough times when he lost both parents within a short time.
"It's sad that he's leaving. Lately, I have seen a different Woody, but when you look at a man in the eyes ... I've seen that look before many, many times, I hated to see it in Woody's. He's a guy everybody has loved and respected."
Rueter won 45 games with the Giants in the 1990s, tops among San Francisco southpaws, and heading into 2005, was fifth overall with a .601 winning percentage by a lefty.
Giants reliever Jason Christiansen said Rueter "has been the poster child for San Francisco pitching over the last nine years, so it's a definitely tough to see him on the way out."
Rich Draper is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.