HERE’s at least one person who will NOT be happy if Katie Couric fills in for Savannah Guth­rie when the “To­day” co-host goes on ma­ternity leave – her longtime nemesis Matt Lauer!

Sources tell The ENQUIRER that Matt “freaked out” when he heard about possible plans to reunite him with his former colleague, even though NBC bosses think the reunion would boost ratings for the troubled NBC morn­ing show. “Today” has taken a beating from ABC’s “Good Morning America” in the last couple of years.

A report in the “New York Daily News” on May 5 said Katie – and possibly Mer­edith Vieira – is being con­sidered as a substitute co-host for Savannah, who is six months pregnant.

Although NBC officials cautioned that there have been no official talks with Katie’s camp, Matt hit the roof at the mere idea of sharing airtime with Katie again, says the source.

“Katie and Matt had a long-running feud behind the scenes, and while Katie has tried to ex­tend an olive branch to Matt in recent years, he exploded and freaked out at the thought of hav­ing her back sitting next to him,” said a source.

While the perennially perky news anchor recently an­nounced that she’d accepted a job as Internet giant Ya­hoo’s “Global Anchor,” the source says Matt doesn’t be­lieve she’s serious about that gig.

Now that her syndicated talk show, “Katie,” is being canceled, Matt thinks she’ll be looking for a steady job in New York once she marries fiance John Mol­ner this summer, according to the source.

“What better job than to be back at the ‘Today’ show – a place she knows like the back of her hand,” the source added. “Matt’s afraid she’ll use the substitute gig to get herself back on the show per­manently.”

Another set insider told The ENQUIRER: “Of course Matt knows Savannah has to take time off to have her baby, but he’s hardly high on Katie returning – and puts Meredith in the same boat.

“While there had been some reports in the media that Katie and Matt had at one point con­sidered co-hosting a syndicated show together, the truth is that Matt still harbors resentment against Katie for a lot of reasons.”

What’s more, Matt’s long-suffering wife Annette Roque has never liked her, especially after Katie admitted to radio shock jock Howard Stern dur­ing an interview that she used to have a crush on Matt.

“Katie may have once been smitten with Matt years ago, but the two had a real ‘love-hate’ relationship dur­ing the years they worked together at Studio 1-A,” said the source.

Katie, 57, was part of the “To­day” show team for 15 years, from 1991 to 2006, before quitting to anchor the “CBS Evening News.” Matt, 56, joined the show in 1997. Together, they delivered record rat­ings for many years, but the bad blood between them was legendary.

While Matt gushed above Katie during her 2006 farewell, a source told The ENQUIRER: “The fact is I think he hates her guts. Matt said that he was sick and tired of playing the straight man for her story set-ups and having to go along with her cutesy ‘I’m-so-innocent’ facade.”

We also reported that when NBC dangled a whopping $100 million, five-year contract in front of Katie in a last-ditch bid to keep her, Matt, who was then earning $9 million a year threatened to walk.

“If Katie does end up back on ‘Today’ when Savannah goes on ma­ternity leave,” said the insider, “rest assured it will be one hot summer between Matt and Katie.”