Acquiring Tumblr won't be quite as simple as shelling out $1 billion. If Yahoo really wants the popular blogging service, it'll have to participate in a royal rumble with Facebook and Microsoft, according to new report from Forbes. Right now, Yahoo is currently in lockup negotiations, meaning Tumblr can't field other offers. But competitors are circling in, putting immense pressure on Marissa Mayer to finalize a deal.

Tumblr has an enormously fervent following of younger teens and adults, a key demographic Yahoo wants to attract as it moves beyond its aging readers. And although Facebook currently has over a billion users on its social network, not to mention Instagram under its belt, Mark Zuckerberg is reportedly interested in an acquisition as well. Microsoft, too, is interested in Tumblr's growing popularity and young followers.

Last year, Tumblr CEO David Karp told Forbes that he was wary of what an acquisition could mean. Karp said he didn't want to sell to a company only to see that company dismantle what he's built. However, if a company bought out Tumblr and merely left the company alone, that's a different story.

Discussions between Yahoo and Tumblr are reportedly so far along that an offer is imminent; Marissa Mayer is waiting on Yahoo's board to approve. "She is said to favor an outright acquisition rather than an investment or partnership," Forbes said. If a deal does go through, Karp would reportedly remain Tumblr's CEO.