"Daniel is a player we have been following for a long time," said the Liverpool boss.
"We first spoke to Brondby about the player when we were in Monaco playing the Super Cup final. At that time, their chairman said he wasn't for sale.
"We scouted Daniel for a long time but then he picked up an injury. When he returned to fitness we watched his first game back and we knew he was at the kind of level we require, even though he played only 25 minutes.
"We've been told he's one of the best centre-halves in Denmark for 20 years. A lot of scouts have spoken highly of him and there has been lots of interest from other clubs.
"People will remember he played particularly well in an international against England earlier this season. We'd already watched and asked about the player before then.
"That match surprised a lot of people, but it confirmed to us he could play at a particularly high level, which is why we've continued to follow him.
"I wouldn't say he was a particularly aggressive style of player. I think he is a very clever type of defender. His positional sense is very good, for example, and he reads the game well. Of course, there are areas he needs to improve, but he is young and we will help him.
"He will be an option for the first team within a short space of time. First he will need to improve his
physical condition but then he will put both Sami and Carra under pressure for their place. This is an area where we've had no competition until now.
"He can't play in the Champions League, but when you sign a player who's only 21 years old, he is for the future of the club, not for a competition in which we have a maximum of seven games left.
"If we have to play seven more games in Europe without players who are cup-tied, it will be a welcome problem."