Claude Puel has insisted he can not change his squad so late in the transfer window, and a potential world-record bid for Harry Maguire would be rejected.
Asked about United's interest, Foxes boss Puel joked with the media at his pre-match press conference.
The 21-year-old scored the victor in the Manchester derby nearly two years ago, and is determined to hit the back of the net at United's home ground again after rediscovering his best form this pre-season.
Puel said: "We have had good speaking with Harry recently and with the chairman also and we can not change our things just before a game and just before the new season, it is not possible for us".
"We found success with good moves and good quality and perhaps in the second-half we had good energy to finish this performance for another result but I think at the end it is a disappointment".
"Harry, he's happy also to remain with us".
With just four days of training behind them Puel has hinted that neither are expected to play at Old Trafford but with the two being so important to his side it is being rumoured that the Frenchman could spring a surprise and play them. He is our best player.
Maguire played for Leicester against United on Friday night.
Meanwhile Croat Benkovic, 21, arrives from Dinamo Zagreb for £13m.
Leicester City are supposedly happy to hold onto Maguire - or let him go - given the fact that they have covered the defender's position should he leave, and have clear reinforcements, should he stay, putting the ball right back into Manchester United's court.
That makes it seven summer signings at Leicester - following Ricardo Pereira, Jonny Evans, James Maddison, Danny Ward and Rachid Ghezzal.