'Today' -- Where In the World Is Matt Lauer ... Seriously

9:15 AM PT -- Sources connected with NBC tell TMZ, "Matt took this exact same week off last year and the year before. And other anchors have taken off in Sweeps months before."

12:30 PM PT -- FOUND YOU!

The "Today" show needs all the firepower it can muster to blunt the return of Robin Roberts on "Good Morning America" during the all-important February sweeps -- but NBC's biggest weapon is missing from its arsenal -- one Matt Lauer.

Sources connected with the network tell TMZ ... Lauer is taking the week off because he wants to spend time with his kids, who are off from school.

It's unheard of for a network anchor to bail during sweeps -- when ratings translate into advertising dollars. As far as we can tell, no anchor on "Today" has ever done it.

We're hearing 2 conflicting stories as to why Lauer is MIA from "Today":

1. NBC knows they're going to get their asses kicked with Roberts' return, and Today without Lauer is a good excuse.

2. Matt just doesn't care anymore.