Former Celtic captain Paul Lambert says he would be "shocked and disappointed" if the club sacked Martin O'Neill, although he admits it would not surprise him if the 74-year-old chose to walk away.
O'Neill plans to use the international break to assess Celtic's situation following a difficult run of results, including consecutive defeats by Rangers.
Those Old Firm losses came either side of a Europa League home defeat by Ferencvaros, while Celtic also suffered a dramatic Champions League collapse against LASK in August after surrendering a 4-0 aggregate advantage.
O'Neill, who returned as permanent manager for a second time during the summer, acknowledged the criticism surrounding his position and admitted questions over whether he can turn Celtic's fortunes around are justified.
His appointment followed two spells as interim manager last season, when he helped Celtic recover from managerial upheaval to secure a league and Scottish Cup double.
O'Neill previously managed Celtic between 2000 and 2005, winning seven trophies during a highly successful spell in which Lambert was part of his squad.
Lambert regards his former boss as Celtic's best manager since Jock Stein and believes O'Neill has built enough credit at the club to decide his own future.
"It wouldn't surprise me if he left. I don't think he needs it," Lambert said.
"I'd be shocked and disappointed if Celtic sacked him.
"He's got enough credit in the bank. It wasn't that long ago people were shouting for a statue for him, so I don't think you can go from one extreme to the other.
"If he wants to go, then he goes himself."
O'Neill twice helped steady Celtic last season following the departures of Brendan Rodgers and Wilfried Nancy, with Lambert insisting there was only one man capable of rescuing the club at the time.
The former Ipswich Town and Norwich City manager also placed responsibility for Celtic's recent struggles on the players following their defeats by Rangers.
Lambert was particularly critical of defender Cameron Carter-Vickers, who spoke about Celtic playing "too random" and needing to follow a tactical "script".
"The players need to take responsibility," Lambert told BBC Radio Scotland.
He argued that players must be capable of solving problems on the pitch rather than constantly looking towards the manager for instructions, describing Carter-Vickers' comments as "bang out of order".
With Celtic struggling for form and O'Neill considering the bigger picture during the international break, uncertainty now surrounds the experienced manager's future.
