Diego Costa
Diego Costa in action for Atletico Madrid. [Reuters]

Chelsea reportedly dispatched scouts to Spain to watch Atletico Madrid's recent Champions League victory over Milan, with Filipe Luis and Diego Costa understood to be the subject of their attention.

Manager Jose Mourinho is already planning reinforcements for next season and signing a top striker and a left-back to replace Ashley Cole are his main summer targets.

According to Spanish newspaper AS, two Chelsea scouts watched Atletico Madrid during the side's victory over Milan, with Costa scoring a brace and Filipe Luis excelling on the left-flank.

Costa is one of the most sought-after strikers around Europe, with Arsenal and United also reportedly interested in acquiring his services.

The Spanish international has scored 22 goals in 27 la Liga games this season, even better than the figures of former Atletico Madrid stars like Radamel Falcao and Sergio Aguero.

With Fernando Torres, Samuel Eto'o and Demba Ba failing to convince Mourinho in his first season back at Stamford Bridge, he is desperately looking for a striker and Costa is reportedly on a short-list of players that also includes Falcao, Edinson Cavani and Jackson Martinez.

Mourinho is also looking for a left-back, as Cole's contract at Stamford Bridge is due to expire in the summer. Having been displaced as first-choice left-back by Cesar Azpilicueta this season, his future at Stamford Bridge looks uncertain.

Filipe Luis has reportedly joined a list of possible replacements that includes Southampton youngster Luke Shaw and Valencia sensation Juan Bernat.

In case Mourinho opts to sign Filipe Luis he will have to fight with Manchester United, as recent reports claimed they tried to secure his services during the January transfer window by launching a £17m bid but the offer was immediately rejected by both Atletico officials and the player.

The Brazilian is considered one of the best left-backs in Europe and has been a pivotal player for Atletico since his £10m move to the Vicente Calderon in 2010 from Deportivo La Coruna.