According to the insider, Grammy execs were ordered to keep Swift, 23, and Underwood, 29, "from crossing paths" at the Feb. 10 show "since they hate each other!"
Says a Swift pal, "Taylor feels Carrie is always rude to her, so she steer clear of her." (A Grammy rep counters, "No requests were received from either artist.")
At last year's Country Music Association Awards in Nashville Nov. 1, co-hosts Underwood and Brad Paisley mocked Swift's recent split with Conor Kennedy.
"The greatest trade of the year had to be the Kennedy family. They somehow traded Arnold Schwarzenegger for Taylor Swift," Paisley joked about Swift dating the 65-year-old bodybuilder's nephew through marriage. "I mean, what they got for that . . ."
But Underwood (married to NHL hunk Mike Fisher since 2010) interrupted her co-host to inform him of Swift's breakup. "What? Why don't I ever hear about these things?" Paisley asked. "I'm the last one to know. Are they ever gonna get back together?"
"Never, never, never," Underwood replied, referencing Swift's No. 1 hit single "We Are Never Ever Getting Back Together. "Never ever."
Swift is set to open the Grammys show at L.A.'s Staples Center Sunday. "What's interesting is we presented this performance to the Grammy committee . . . and they said, 'Okay, cool, you have a performance spot.' And then like a week ago they call us and are like, 'Oh, by the way, you're opening the show,'" Swift told Ryan Seacrest Thursday, Feb. 7. "It's not like they approach you . . . It just surprised me I was going to go first."