Gary Patterson is poised to take his TCU Horned Frogs, last season’s Rose Bowl champions, to the Big 12 Conference before they ever play a game in the Big East. (Matt Strasen/AP)

Four days after presidents of the remaining Big East schools voted unanimously to rebuild through aggressive expansion, the league found itself braced for yet another defection, with Texas Christian poised to bail for the Big 12 before its much ballyhooed membership took effect.

Confirmation of TCU’s change of heart wasn’t expected until Friday, when university officials were to vote on accepting the Big 12’s invitation. But Big East officials on Thursday began informing current and prospective members — Navy, among them — of TCU’s decision to renege on its pledge to join the league next year.

It will cost the Horned Frogs $5 million, the Big East’s current “exit fee,” but they’ll be allowed to leave at once, granted a reprieve from the customary 27-month waiting period.

TCU’s departure, though, will cost the Big East in terms of the prestige it has long sought in football and the stability it has so desperately sought sinceSyracuse and Pittsburgh announced Sept. 17 that they were leaving for the ACC.

Without Rose Bowl champion TCU, the Big East will be reduced to just six football-playing members once Syracuse and Pitt depart in 2014. That’s two shy of the NCAA minimum for classification in the college football’s most elite ranks, the Football Bowl Subdivision.

Chet Gladchuk, athletic director at Navy, which tops the Big East’s list of expansion targets, put it bluntly when asked how TCU’s retreat would affect Navy’s interest in the league.

“As I said from the beginning, our position remains comfortable as an independent,” Gladchuk said in a telephone interview. “We’ve had discussions with the Big East about possible membership. There is no timetable or sense of urgency on our part.

“We asked the Big East to stabilize. Obviously this is a step back for them. As it stands today, the issue is not ours. The issue is theirs. They’ve got to figure out how to right the ship.”

For Big East Commissioner John Marinatto, the challenge of “righting the ship” is more complicated than simply replacing the three schools the conference has lost in the last three weeks. It also means staving off further defections, with Louisville and West Virginia, the last two Big East schools to win a Bowl Championship Series game, perceived as receptive to overtures from more established football conferences.

“We’ve got our work cut out for us,” conceded Notre Dame basketball Coach Mike Brey, in Washington on Thursday to promote the Dec. 4 BB&T Classic, in which the Irish will face Maryland. “Some of our football programs in the Big East are looking elsewhere. I think we have to really come up with a plan to make it enticing enough for them to stay. And we have to do a good job of getting some new members — Army, Air Force, Memphis — things like that.”

If the Big East can keep Louisville and West Virginia in the fold and add at least two new football-playing schools, the league can likely weather the losses of TCU, Syracuse and Pitt.

Of the six football-playing schools in the Big East that will remain once Syracuse and Pitt depart, four have been to a BCS bowl game in the last seven years: Cincinnati (2008, 2009), West Virginia (2005, 2007), Louisville (2006) and Connecticut (2010).

But its troubles will be vastly compounded — and its very viability as a football conference will be in question — if the defections mount.

For starters, the Big East will have trouble convincing new schools to join if its own membership keeps hemorrhaging.

Moreover, if it can’t reload with a credible lineup of eight football teams, the Big East’s status as one of the six conferences to boast an automatic berth in one of the big-money bowl games could be in jeopardy.

The criteria for losing automatic-qualifying status for the BCS are apparently as murky as the criteria for getting one. The only non-negotiable requirement is that an FBS conference must have eight members. The NCAA permits a two-year window in which a conference can fall short without losing its FBS status. (In the case of the Big East, the clock would start ticking in 2014, when Syracuse and Pitt depart, giving the league until 2016 to reach the threshold.)

East Carolina is among them. Its athletic director, Terry Holland, said Thursday that TCU’s departure didn’t deter its interest at all.

East Carolina, which competes in Conference USA, could help the Big East replace the mid-Atlantic foothold it lost when Virginia Tech left for the ACC in 2005, Holland said, noting that the Pirates had been to five consecutive postseason bowls and won two C-USA championships in that time.

Temple could also make a compelling case for rejoining the Big East given its resurgence in football, its strong basketball tradition and its ready-made rivalry with crosstown Philadelphia foe Villanova. Similarly, the addition of Central Florida could leverage the Big East’s investment in South Florida.

As for Louisville and West Virginia, Pilson asked rhetorically, “Do they have any place to go?”

“At this point, probably the Big East is their best option,” Pilson said. “It’s all a game of checkers and dominoes right now.”

Missouri may be the next piece on the game board to move, rumored a target of the 13-member Southeastern Conference, which would likely trigger another rash of conference-jumping.

Staff writers Gene Wang and Kathy Orton contributed to this report.