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Concern has emerged that the future viability of Conference USA is "hanging on by a thread" as college football conference realignment continues to play out, sources tell CBS Sports. At issue is what appears to be the impending defection of three Conference USA schools ot the Sun Belt. Southern Miss accepted a Sun Belt invitation on Friday, while Marshall and Old Dominion have yet to formally decide. Those schools, along with FCS power James Madison, are expected to be invited to join the Sun Belt as early as next week.

Should Marshall and Old Dominion join Southern Miss in departing, Conference USA would be reduced from eight to five members, putting the league in dire straits. At least six members of a conference are needed to determine a league champion to earn an automatic berth into the NCAA Men's Basketball Tournament.

CBS Sports previously reported James Madison was choosing between Conference USA and the Sun Belt with its decision potentially determining the future of Old Dominion and Marshall.

Conference USA lost six of its 14 members on Thursday when CharlotteFlorida AtlanticNorth TexasRiceUAB and UTSA announced that they were joining the American Athletic Conference. It is believed they will start playing in the AAC as soon as the 2023-24 athletic season. 

Should Conference USA lose the three aforementioned programs and ultimately dissolve, the result would be the number of FBS conferences shrinking from 10 to nine. That could potentially impact ongoing talks regarding College Football Playoff expansion. As proposed, the top six ranked conference champions would receive an automatic berth in a hypothetical 12-team bracket, but that's based on the 10 existing leagues continuing

The 26-year-old league could be the first FBS conference to fold since the Big East in 2013 with the football remnants of the old Big East eventually serving as the foundation for the AAC. Prior to that, the last FBS -- then Division I-A -- conference to go away was the Southwest Conference in 1995.

Decisions could be made in the next three days, sources tell CBS Sports. As such, Conference USA faces the prospect of losing nine of its 14 members within in a week. At that point, the league's future would be decided by its worth to media rights holders. If a collection of teams in the newly-formed C-USA does not draw enough interest from networks, it could go away completely. The C-USA television deal with CBS expires after the 2022-23 academic year, and the conference also has separate deals with Stadium and ESPN (mostly streaming on ESPN+).

"To say that [Conference USA] is not wounded would be to deny [reality]," a source close to the discussions tells CBS Sports.

Something working in Conference USA's favor is the $4 million exit fee. If nine schools ultimately leave, that would add $36 million in the coffers to help entice new members. C-USA commissioner Judy MacLeod has been frantically trying to keep her existing members together while reaching out to candidates to replace departing programs, multiple sources tell CBS Sports. 

"We have a strong core of members to build around and are continuing to work to strengthen our league as we move forward. There are several institutions interested in joining Conference USA, both across FBS and FCS, some of whom we've already met with in person," said MacLeod in a Friday afternoon statement. "Every step we take will be deliberate, strategically sound, and intentional. We will take the necessary time to add future members that will be the best fit from an athletic and academic standpoint and allow prospective institutions time to complete their process.

"We continue to believe in the regional concept and will look to incorporate that into our structure and scheduling. There are certainly many questions out there, but a great deal is happening behind the scenes. When appropriate, we will release more information, though out of respect for those involved, we will continue to operate outside of the public space."

There has been contact between Conference USA and McNeese State from the Southland Conference and Sam Houston of the WAC, sources tell CBS Sports. Like James Madison, those FCS schools would require an NCAA-mandated multi-year transition process to move up to the FBS.

"She's getting calls from every aspiring FCS program," a source from one of those schools said.

The preference for Conference USA is to add FBS members with schools such as independents New Mexico State, UConn and UMass. CBS Sports previously reported independent Liberty is in the mix for either Conference USA or Sun Belt membership. Given the developments of this past week, Liberty would likely prefer the Sun Belt at this time as the school assesses its options.

In terms of competition and revenue, it's basically a wash for any of the candidates in Conference USA and Sun Belt, and the decision may come down to travel expenses. The 10-team Sun Belt could evolve as an East Coast league with the addition of more schools within that region. In inviting any members, C-USA still has to deal with the existence of far-flung UTEP, which is 900 miles from the nearest current member, Louisiana Tech.