The Portuguese boss has been frequently linked with a return to the Blues to replace current interim manager Rafael Benitez, whose contract expires in May.
While Buck says that Chelsea are considering a number of options he admits that Mourinho, who is widely expected to leave Real Madrid in the summer, could still return to the Londoners.
Asked if anyone had been ruled out of the running, Mourinho in particular, Buck said: "I am completely open minded about it.
"We really haven't started [the hunt for a new boss] yet but we're all thinking about it and have some ideas, and certainly Mr Abramovich is thinking about it.
"At the moment, we're concentrating on the end of the season."
Mourinho won two Premier League titles during his first reign at the club.