Yasin's killing is no longer a question of legitimacy for Israel but a matter of opportunity and "interest", the general told Israel's Channel 2 television on Monday.
Yaalon accused Shaikh Yasin of having "personally ordered" last Wednesday's Hamas resistance attack at the Erez crossing between the occupied Gaza Strip and Israel that killed four Israelis, three of them soldiers and the other a security guard.
Hamas warned on Saturday that Israel would "drown in a sea of blood" if it tried to kill the elderly paraplegic founder of the Palestinian resistance group.
"Israel will pay a high price for any attempt to hurt Shaikh Yasin or any other Hamas leader," Izz al-Dine al-Qassam Brigades, the armed wing of Hamas, said in a statement.
The warning was in response to a veiled threat by Israel's deputy defence minister Zeev Boim to resume the policy of assassinating Palestinian resistance activists.
Palestinians and the international community have condemned Israel's policy of targeted assassinations.