The East Midland's side are on the verge of a huge coup, by signing Portuguese under-21 international Carvalho in a move that would more than double the club's transfer fee record.
The Benfica player is highly rated, having represented his country at every level.
The 21 year-old midfielder, who is represented by Portuguese super-agent Jorge Mendes is expected to be joined at the City Ground by his teammate Diogo Goncalves, with the latter joining on a season-long loan.