A frustrated Eriksson was disappointed his side could not build on their midweek win at Leeds after going down 2-0 at high flyers Swansea.
Debutant Marvin Emnes came off the bench to break the deadlock five minutes after half-time before Scott Sinclair secured the three points, Emnes - again involved, picking out Sinclair to finish from six yards as the Foxes chased a late equaliser.
The former England boss said: "It wasn't a good afternoon for us - it was a step back from Tuesday night when we beat Leeds.
"We have to work hard and get better because if we keep on losing we can forget about the play-offs or promotion."
Eriksson will be eager for his Foxes to bounce back as they turn their attention to their midweek Carling Cup home tie against West Brom before returning to Championship action at home to Preston.
Eriksson added: "We will start work for the Carling Cup game on Tuesday and then we have Preston at home on Saturday, which is a big game for us.
"We created chances and maybe we should have scored, but their keeper made a few fantastic saves. But when you look at the game, Swansea were the better team and thoroughly deserved to win.
"They were absolutely the better team, especially in the first half and parts of the second. We came back hard in the second half to try to get a draw."
Source: PA