"I think Imus is done," CNBC's Donny Deutsch told "Power Lunch" before the MSNBC announcement.
American Express also cancelled its advertising with Imus, the Wall Street Journal reported.
The yanked ads compounded the fallout that began when the now-suspended radio show host called players for the Rutgers University women's basketball team "nappy-headed hos" on his April 4 show.
"General Motors obviously does not condone the comments Don Imus recently made in reference to the Rutgers University women’s basketball team," the company said in a statement.
GM acknowledged Imus' apology and said it supports the disc jockey's charitable efforts for children with cancer and autism.
Late Tuesday, Procter & Gamble became the third advertiser publicly known to have pulled its ads, joining Staples and Bigelow Tea.
P&G spokesman Terry Loftus said the company pulled ads from the show as of last Friday.
The Wall Street Journal reported that P&G pulled its ads from all daytime programming on MSNBC television, which carries Imus' show. MSNBC sells ads for full daytime hours rather than around specific programs, so P&G yanked all daytime ads.
"Because of the recent comments that were made on the program it did prompt us to take a look at our decision to advertise on the program and we have decided to stop advertising," Staples spokesman Paul Capelli said Tuesday night.
"Once we became aware of the comment, we sort of stepped back and took a look at it," he said, declining to disclose the dollar amount of the advertising involved. "We weren't on today and are not planning on being on going forward.
"I can't speculate on what we might do in the future," he said.
Another sponsor, Bigelow Tea, said in a statement posted on its Web site that the remarks have "put our future sponsorship in jeopardy."
Calls for the radio host's dismissal have been growing, including from groups such as the National Organization for Women and the National Association of Black Journalists.
The 10 members of the Rutgers team spoke publicly for the first time Tuesday about the on-air comments, made the day after the team lost the NCAA championship game to Tennessee.
Some of them wiped away tears as their coach, C. Vivian Stringer, criticized Imus for "racist and sexist remarks that are deplorable, despicable, abominable and unconscionable." The women, eight of whom are black, called his comments insensitive and hurtful.
"It kind of scars us. We grew up in a world where racism exists, and there's nothing we can do to change that," said Matee Ajavon, a junior guard. "I think that this has scarred me for life."
The women agreed, however, to meet with Imus privately next Tuesday and hear his explanation. They held back from saying whether they'd accept Imus' apologies or passing judgment on whether a two-week suspension imposed by CBS Radio and MSNBC was sufficient.
Rutgers' athletic director, Robert E. Mulcahy III, thought a meeting with Imus would offer the team's players a chance to listen to him and hear what he has to say. Several players said they wanted to ask the host why he would make such thoughtless statements.
"We all agreed the meeting with Mr. Imus will help," said Essence Carson, a junior forward. "We do hope to get something accomplished during this meeting."
In Washington, White House spokeswoman Dana Perino was asked if the president thought Imus' punishment was strong enough, but said it was up to Imus' employer to decide any further action.
"The president believed that the apology was the absolute right thing to do," Perino said Tuesday.
Imus' radio show originates from WFAN-AM in New York City and is syndicated nationally by Westwood One, both of which are managed by CBS Corp. . MSNBC simulcasted the show on cable. MSNBC television and MSNBC.com are joint ventures of Microsoft and General Electric's NBC Universal News. General Electric is also the parent of CNBC.com.
While Imus has used his show to spread insults around - once calling Colin Powell a "weasel" and another time referring to New Mexico Gov. Bill Richardson as a "fat sissy" - his comments about the Rutgers women crossed the line, Stringer said.
"It is more than the Rutgers women's basketball team. It is all women's athletes. It is all women," said Stringer, the third-winningest women's basketball coach of all time who has taken three teams to the Final Four.
Imus has apologized repeatedly for his comments. He said Tuesday he hadn't been thinking when making a joke that went "way too far." He also said that those who called for his firing without knowing him, his philanthropic work or what his show was about would be making an "ill-informed" choice.