The fullback's season is over after being injured last week against Arsenal.
After their FA Cup win against Barnsley last night, Slot said of Bradley's setback: "First of all, let's talk about him because Trent (Alexander-Arnold) was leaving and Conor Bradley already replaced him last season really well a few times.
"I think the year before I came (he) also had a good spell. So, I think he felt - and I felt the same - this is now going to be your time and then he missed out on so many games because of injury already, because of mainly hamstring injuries.
"Coming back from that, being in the team, progressing, doing better and better, staying fit and then something like this happens. In a season where he thought before it started, 'This has to be my season' and I thought the same, to maybe play six, seven or eight games is a big, big, big blow for him and I also think about Northern Ireland, where he is trying to reach the World Cup.
"So, it's an enormous blow for him, but as a result of that it's a big blow for us as well because I hope that you don't think I would like to play Dominik Szoboszlai as a right full-back. Jeremie Frimpong has to play a lot of minutes, also comes back from an injury, has missed out on three or four months of a lot of playing time.
"I liked him again today, by the way, but I have to make sure he is able to play again at the weekend and then we go to Marseille and then we go to Bournemouth. It is nine games in January with six defenders available. I have to manage it in the right way and I have to give enormous compliments to the players that are fit that we are 11 games unbeaten."