Liverpool are to complete the £5.8 million signing of the Denmark international Daniel Agger today, ending a four-month pursuit of the Brondby defender and strengthening the European champions' options in the centre of their back line.

Agger will complete the formalities of his medical at Melwood today and sign a four-year contract, having pulled out of the Brondby squad that left for a winter training camp in Gran Canaria yesterday.

Instead, the 21-year-old flew to Merseyside after lengthy negotiations between the two clubs eventually reached agreement on the size of the fee.

The signing will complete Rafael Benitez's search for a third centre half to challenge Jamie Carragher and Sami Hyypia for a starting place.

Though there were talks with Spartak Moscow with a view to signing Nemanja Vidic, who instead went to Manchester United for £7 million last week, and with Deportivo la Coruna about a possible move for Cesar or Fabrizio Coloccini, Agger was quickly established as Liverpool's first choice.

"Daniel is a player we have been following for a long time," said Benitez, who will add Agger to the Dutch international right-back Jan Kromkamp, signed from Villarreal, as his transfer-window defensive recruits.

"We first spoke to Brondby about the player when we were in Monaco playing the Super Cup final in August.

"At that time their chairman said he wasn't for sale. We continued scouting 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.

"People will remember he played particularly well in an international against England earlier this season, but we'd already watched and asked about the player before then."

Denmark won that match last August 4-1, with Agger's performance attracting similar interest from Bayern Munich, Juventus and Everton, though only Liverpool lodged a firm bid.

The young centre back will be ineligible for Liverpool's defence of their Champions League title having featured for Brondby in the Uefa Cup already this season. Benitez is confident, however, that he will be ready to play in the Premiership.

"The England match surprised a lot of people but it confirmed to us Daniel could play at a particularly high level, which is why we've continued to follow him," the manager said.

"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 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 in 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 places. This is an area where we've had no competition until now."

Denmark's head coach Morten Olsen said he believed that Agger was good enough to make a big impact.

"He is confident about what he can do at the moment - he still has something to learn and he has a good mentality and if he goes to Liverpool I can only say they will have a top-class player.

"He certainly has to play 25 games because only in that way will he become a better player, and he is only 21 so he is not a player for the bench.

"Of course he has got to accept he maybe cannot play in the first team in every game but I am sure he will show that he is a top-class player."

"(This is a good move) for Daniel Agger and for the Danish national team because the Premier League is a top-class league."