Diplomats told Reuters that veteran Algerian diplomat Lakhdar Brahimi could be named next week to replace the U.N.-Arab League Syria envoy Kofi Annan, who resigned in frustration at the international deadlock on how to end the violence.
But they warned there could be last-minute changes if a key government had concerns or the candidate had second thoughts.
Assad, engaged in an all-consuming fight with his mostly Sunni opponents, appointed a Sunni as his new prime minister on Thursday after his predecessor fled on Monday in the highest-level defection so far in the uprising that began 17 months ago.
Wael al-Halki, from the southern province of Deraa where the revolt began, replaces Riyad Hijab, who had spent only two months in the job before making a dramatic escape across the border to Jordan.
Assad's authority was already shaken by the assassination last month of four of his top security officials and by rebel gains in Damascus, Aleppo and swathes of rural Syria.
But he has persevered with a crackdown on opponents seeking to end half a century of Baathist rule and topple a system dominated by members of the president's minority Alawite sect.
He has focused his fierce army counter-offensive on Syria's two main cities, reasserting control over much of the capital Damascus before taking the fight to the northern commercial hub.
Rebels fighting in the Aleppo district of Salaheddine, a southern gateway to the city, said they had been forced to fall back from frontline positions on Thursday by a fierce bombardment which had reduced buildings to rubble.
"There have been some withdrawals of Free Syrian Army fighters from Salaheddine," rebel commander Abu Ali said. Others said the main frontlines in the area, which had been held by rebels for more than a week, were now deserted.
