Fredy Guarin and Mauro Icardi could be sold in the January transfer window to raise funds.
But Mancini says: "I don't think it will happen. In fact, we need to bring in a few players that we're missing. I am convinced this side will challenge for the Champions League.
"It is the first time I have seen my lads absorb so much information so quickly. I am convinced we will fight for third place and for victory in the Europa League.
"The locker room mustn't get knocked down, we need joy in there. This is the foundation for doing well."