The Big 12 announced earlier on Thursday that it is in discussions to add TCU to the conference.
TCU would become the Big 12's 10th member.
Texas A&M is heading to the SEC in July and the future of Missouri is uncertain after the school announced Tuesday night that it was exploring its options related to conference affiliation.
TCU was set to join the Big East in July, but that appears to be very unlikely after Thursday's developments.
"Acting upon a unanimous recommendation of its expansion subcommittee, the Big 12 Conference Board of Directors has authorized negotiations with Texas Christian University to become the Conference's 10th member, and instructed interim commissioner Chuck Neinas to immediately begin discussions with TCU," the Big 12 said in a statement.
"The action of the Board was without dissent. On the advice of legal counsel, The University of Missouri did not participate in the vote."
TCU also confirmed having discussions with the Big 12.
"These discussions with the Big 12 have huge implications for TCU," TCU Chancellor Victor Boschini Jr. said in a statement. "It will allow us to return to old rivalries, something our fans and others have been advocating for many years.
"As always, we must consider what’s best for TCU and our student-athletes in this ever-changing landscape of collegiate athletics. We look forward to continuing these discussions with the Big 12."
TCU makes perfect sense for the Big 12. It is a great geographic fit and the Horned Frogs would instantly establish rivalries with schools like Texas and Texas Tech. Plus, TCU has become a football power. The Horned Frogs beat Wisconsin to win the Rose Bowl in January. Adding TCU would certainly strengthen the Big 12's football reputation.
If TCU does indeed join the Big 12, it would be yet another crippling blow to the Big East. Pittsburgh and Syracuse announced last month that they were leaving the conference to join the ACC. With Pittsburgh and Syracuse leaving and TCU potentially bolting to the Big 12, the Big East would be left with six football-playing schools.