Hezbollah terrorists and Israel fought a devastating conflict in 2006, and the Lebanese Shiite group is currently backing President Bashar al-Assad's regime in the Syrian civil war.
Both countries border Israel to its north.
"In the next war in the north of the country, Lebanon will not be the only front," Liberman said in a speech to soldiers.
Liberman added that the Lebanese army had lost "its independence by becoming an integral part of Hezbollah, which gives it its orders."
Israeli leaders frequently warn Lebanon that the country's army and civilian infrastructure would be overwhelmingly targeted if Hezbollah attacks from civilian areas. Hezbollah is also supported by Iran, Israel's arch-enemy, which backs Assad in Syria as well.
Israel's military believes Hezbollah has between 100,000 and 120,000 short- and medium-range missiles and rockets, as well as several hundred long-range missiles, with the medium-range missiles capable of reaching Tel Aviv.
Liberman evoked the possibility of a simultaneous conflict in the north and in the south with Hamas in the Gaza Strip.
"The battle will take place on the northern and southern fronts," he said.
"There is no longer war on one front. It's our basic assumption and it is what our military is preparing for."
Since 2008, Israel has fought three wars with the Hamas terrorist organization, which also receives support from Iran.
Israel has sought to avoid becoming involved in the Syrian civil war, but acknowledges carrying out dozens of air strikes there to stop what it says are advanced weapons deliveries to Hezbollah.