Real Madrid have stepped up their tracking of Bayer Leverkusen midfielder Florian Wirtz, a source has told ESPN, with concerns over Madrid's creativity following the retirement of Toni Kroos.

ESPN reported last week that Madrid were considering strengthening their defence in the January window, and are monitoring Liverpool right-back Trent Alexander-Arnold.

However, several voices within the club have also pointed to the need to sign a ball-playing midfielder, after Madrid decided not to look for a Kroos replacement in the summer.

A source told ESPN that making a signing like Wirtz in January would be difficult, given the kind of transfer fee Leverkusen would expect to receive.

However, Madrid want to keep a close eye on Wirtz with a view to signing him next summer, believing him to be an interesting prospect given his age, profile and potential.

At 21, Wirtz has already been a key part of a Bayer Leverkusen team -- coached by Xabi Alonso -- which won a Bundesliga and cup double last season, and was called up by the German national team to play in last summer's European Championship.

Sources close to Madrid's coaching staff have told ESPN that they are unhappy with the make-up of the midfield, and believe that a player with Wirtz's skillset would offer a different profile to those of Eduardo Camavinga, Aurélien Tchouaméni and Federico Valverde.

Nonetheless, they believe the squad -- including veteran Luka Modric, Dani Ceballos and Arda Güler -- can still contibute to improved performance in the coming months.

Madrid have been monitoring Wirtz since last season, and a source has told ESPN that their tracking has intensified in recent months.

The LaLiga giants have received good reports on the German international, and now want to see how he develops in an elite competition like the Champions League, given that last season he only featured in the Europa League.

Madrid value the balance Wirtz offers Leverkusen in midfield, as well as his ability to get into the opposition penalty box.

In 10 Bundesliga games this season he has scored four goals and provided two assists, while in the Champions League he has scored three goals in four games.