CBS Facing Possibility of Losing a Signature Event

But the stability perpetuated by Sean McManus since he became the president of CBS Sports in 1996 could be jarred within the next few months if the N.C.A.A. opts out of the final three years of its tournament deal with the network.

As McManus prepared to watch Duke’s 61-59 victory over Butler on Monday night, he knew he might have been watching the end of March Madness on CBS.