The Trotters were left shell-shocked at the Madejski Stadium as Adam Le Fondre scored three in the Royals' rout to increase the pressure on Wanderers boss Dougie Freedman.
It means Bolton remain just four points above the drop zone - after a disastrous start to the campaign - and facing the very real prospect of two relegations in three seasons if things do not improve quickly.
Their attention will first turn to the FA Cup, though, with Cardiff heading to the Reebok Stadium this Saturday and Spearing eyeing an instant response.
"We, as players, have to stand up and take responsibility because we haven't been good enough," the former Liverpool midfielder admitted to Wanderers' official website.
"I'd like to apologise to the fans. Not one of us were anywhere near our best.
"As a group of players, our mental strength has to improve. We're in it all together and we've got to hang in there. We've now got to move on and get on with it. There's nothing we can do about the game now.
"There are no positives to take from the game, it's as simple as that. We have to put it behind us and look to really improve ahead of the FA Cup game against Cardiff.
"Right now, it's very difficult to take, but we can't feel sorry for ourselves. We'll be straight back in training trying to put things right."