Leicester City manager Nigel Pearson admits his side's workrate at crucial points in the game is a concern.
The Foxes were beaten 2-1 at struggling Doncaster last weekend and are now five points adrift of the play-offs.
Pearson told BBC Radio Leicester: "We are not working hard enough at crucial times in the games.
"We have a bit of a soft underbelly at the moment and that's a game we should have won. I have to change the mentality of some of the players."
Leicester had a 1-0 lead at half-time but two goals from Billy Sharp in three minutes after the break secured Doncaster's fifth win of the season.
"In all honesty that is another game I would've been disappointed to draw," added Pearson.
"To lose, it shows clearly we are not moving forward at the moment. We will do but there may have to be one or two changes.
"In terms of getting in front and in control of the game, to allowing the opposition to get on top, suggests we have quite a bit of work to get this team into shape and challenging."