The Merseyside outfit slipped to a 3-2 defeat to the League One side at Boundary Park on Sunday afternoon, ending their dreams of a return to Wembley.
And the Scotland-born former Republic of Ireland international believes the entire squad must be reminded of their responsibilities by boss Brendan Rodgers.
"It is a huge defeat and, for a club like Liverpool, it is a bit embarrassing," he told the Irish Independent. "Two things come out of it when you play fringe players.