Tottenham managed to hold on to Modric this summer despite receiving at least three offers for the Croatian, the biggest reported to have been ?40million.
"We won't be selling our best players or anyone we want to keep in January," Redknapp said. "We are keeping our best players and if anything we will be adding to the squad not selling."
Despite pleading to move to Stamford Bridge, Modric remained at White Hart Lane in the summer, and he has since gone on to play a big part in helping the club go on the 11-match unbeaten run which has catapulted them to third in the Barclays Premier League.
Redknapp added: "That's the message from me and the chairman [Daniel Levy]. We won't be weakening this squad. If one or two positions open up where fringe players want to go then we will look at that but we are not going to sell our best players or anyone we want to keep."
Redknapp's admission that he could be willing to let a couple of fringe players go is likely to fuel speculation over the likes of Roman Pavlyuchenko, Heurelho Gomes and Sebastien Bassong.
All three want to leave to get more first-team football, and Redknapp has been linked with a number of replacements already. The Spurs boss would not rule out bids for Bolton defender Gary Cahill or Chelsea's transfer-listed duo Nicolas Anelka and Alex.
"Alex is good player but he is not a player who we have made enquiries for," Redknapp said.
"I've always been a big fan of Gary Cahill. I have tried to sign him a few times. He is a good signing for somebody if he leaves.
"Anelka is a good player as well. All three are good players. I wouldn't sit here and say I wouldn't be interested in any of them. It depends on what happens here."
Source: PA
Source: PA