Joe Scarborough is under intense pressure to perform as he goes head-to-head with old foe Don Imus.

MSNBC chiefs have been nervously watching the ratings since Imus’ show on the Fox Business Network started airing at the same time as Scarborough’s “Morning Joe” earlier this month.

Scarborough was hit with a further blow this week when his radio show was dropped by DC radio station WMAL.

A source told Page Six: “Those higher up at MSNBC are unnerved by Imus’ move to Fox Business Network and fear his show could push Scarborough down. They’re putting a lot of pressure on Joe to keep the ratings up. To make things worse, there are multiple scores to be settled.”

Tom Bowman, Imus’ old producer at MSNBC, jumped to Fox Business with him, and is said to have harsh feelings toward Scarborough and his executive producer, Chris Licht. “So they [Imus and Bowman] are out to win,” said our source.

The simulcast of the “Imus in the Morning” syndicated radio show was dropped by MSNBC two years ago after Imus called the Rutgers women’s basketball team “nappy-headed ho’s.” Scarborough said at the time, “Don Imus always hated my guts . . . he called me ‘Banjo Boy.’ ”

Early ratings showed Imus gave the Fox Business Network a boost in his first week on air, averaging 148,000 viewers a day, a few thousand viewers ahead of CNBC. But “Morning Joe” remained ahead, averaging 357,000.

Scarborough and his team are keen to play down the rivalry with Imus, and Scarborough has been busy focusing his fire at Fox News’ host Glenn Beck. A source close to Scarborough told us, “Imus is not even on our radar. Joe is too busy concentrating on what he is doing,”

An MSNBC spokeswoman said Imus’ show “has had no impact on ‘Morning Joe’ ratings or guest bookings.” Fox Business Network and a rep for Imus declined to comment.