As you cleaned and lubed afterward I am assuming that you did not do any BB or pedal work just before the problem occurred. Given that I second FB's advice, and would emphasize that you need to do the procedure to both pedals, as sometimes a click can be caused at the point where pressure is released, rather than when it is applied. Tightening the crank arms may also be needed, but use care not to gorilla-wrench it. A standard length ratchet and properly sized metric socket will do it fine. If it still clicks you are into some detective work - or a shop is.