NBC is clearly a troubled network, following three years of declining ratings, a loss of more than $1 billion in upfront revenue the past two years, and yet another fourth-place season finish.

Now, it's poised to boot Kevin Reilly, the well-regarded NBC Entertainment president, as part of a shakeup on the eve of this year’s upfront buying season.

The ouster is a surprise, coming on the very eve of the annual upfront market. Reilly has been with NBC for four years and just signed a three-year contract extension in March.

The move, which was leaked over the long holiday weekend, comes after the poor reaction among media buyers to the network's fall lineup up, which is heavy with sci-fi series, in the mold of "Heroes," its one hit last season.

Buyers have criticized NBC for making too few changes after a disastrous season and for targeting hard-to-reach men 18-34 over the broad audience it needs to attract to revive its ratings.

Reilly is taking the rap, and the network has begun seeking out a replacement.

The reported frontrunner is Ben Silverman, head of the TV studio Reveille Productions, which has produced recent broadcast hits like “The Office” and “Ugly Betty.”

Other candidates include Reilly’s No. 2, Katherine Pope, as well as USA Network head Bonnie Hammer, NBC cable head Jeff Gaspin, and even former Fox Entertainment president Gail Berman.

The network is expected to announce a successor sometime this week. There are also rumors flying that Reilly himself may resign today.

The new entertainment president will also likely add oversight of the network’s studio. That’s important because NBC, as part of several greater cost-cutting measures, has become more dependent on NBC Universal Television Studio over the past two years. This year, it only ordered comedy pilots from NUTS.

While Reilly has certainly had his ups, among them the surprise success of “Heroes,” this season’s only breakout new hit, he’s also overseen a number of disappointments.

The network has struggled to find a winning Thursday lineup after the departure of “Friends.” It paid millions for rights to high-profile flops like “The Contender” and “Studio 60 on the Sunset Strip,” and its primetime average fell 6 percent this year compared with last among 18-49s, to a 3.1 rating.

During May sweeps, its average plunged 22 percent.

But many of Reilly’s supporters argue that he is simply the fall guy for problems that reach higher into the NBC organization.

To his credit, Reilly smartly stuck by the NBC tradition of valuing quality programming above all else, renewing low-rated but critically acclaimed programs like “Office,” “Friday Night Lights” and “30 Rock.”

And many believe he was never given the free rein, or for that matter the time, to rebuild NBC's primetime schedule.

During his first years, there was the sense that former NBC entertainment president Jeff Zucker, who had moved above him, was still making most of the big decisions. Critics blame Zucker for many of the bad programming decisions that led to NBC's ratings tumble in the first place.

Further, Reilly was forced to work with budget cuts on the part of NBC that forced him into difficult decisions, such as relying on reality and game show programming during the 8 p.m. hour to keep production costs down.

Reilly's replacement may have better luck if, as reported, that person gains control of the studio as well, giving him or her more control over pilot development and ideally a more diverse lot of pilots to choose from.

NBC has not commented on the rumored shakeup, but an announcement must come soon, as media buyers ready for upfront negotiations. There could be some schedule changes once the new entertainment president is in place.