Under Nancy, Celtic shipped 18 goals, one more than they had conceded during the opening 24 games of the season.
“He was One-Way Will, 3-4-3, I’m not going to change,” former Celtic striker Chris Sutton told 5 Live Sport’s Monday Night Club.
“He needed to adapt. Celtic have played with a back four as long as I can remember and he came in halfway through the season, with a squad which, in truth, is pretty incapable, and trashed the team.
“While some of the football was good on the eye, Celtic were far too patchy. It was kamikaze stuff.”
O’Neill, who managed the club from 2000-05, had been placed in temporary charge after Brendan Rodgers, who was appointed manager of Saudi Pro League side Al-Qadsiah last month, resigned in October.
Having previously managed rivals Montreal, Nancy led Columbus to the MLS Cup in 2023 and then the Leagues Cup – a competition between Mexican and American sides, as they finished second in the league.
However, after being named MLS manager of the year for 2024, his side slipped to seventh in Eastern Conference and 12th overall last year.
As he leaves Celtic, Nancy has enjoyed just five wins in his latest 20 games as a coach.
Serving from June 1999 to February 2000, John Barnes had previously been Celtic’s shortest serving permanent manager, overseeing 29 matches in his eight months.
