Chelsea Transfer News: Latest on Diego Costa and Jackson Martinez Rumours

Chelsea have reportedly turned down an approach from Atletico Madrid over the availability of their former striker Diego Costa, but the Blues themselves are interested in the Spanish club's Jackson Martinez.

According to John Cross in the Mirror, Atleti boss Diego Simeone made a "cheeky move" for Costa, 27, but he was knocked back by the Blues.

The Spanish forward's future has been questioned in recent months after his poor return in 2015, and Bleacher Report's Dean Jones recently predicted that he would be back at the Vicente Calderon soon:

Costa's poor form in front of goal has been one of many negatives in Chelsea's terrible 2015-16 season—the defending champions sit 14th in the Premier League—and he has looked disinterested at times this term.

However, he has scored three of his six league goals this season in his last two appearances, perhaps an indicator that he is returning to some kind of form, per WhoScored.com. 

Clearly Simeone believes Costa still has something to offer his goal-shy Atletico team who, despite being top of La Liga, have scored 15 fewer than second-placed Barcelona and 22 fewer than third-placed Real Madrid.

Their £25 million summer signing from Porto—Martinez—has been disappointing, netting just two La Liga goals in 13 appearances, per WhoScored.

Cross indicated Chelsea are interested in signing the Colombian, perhaps on a loan deal, but Atleti will not let him go unless they can bring someone else in.

Martinez's agent, Henrique Pompeo, previously failed to deny the interest from Chelsea and did not rule out his client potentially leaving Madrid, per Spanish outlet AS (via Sky Sports' Nick Lustig):

"I can't say it's a lie, this is football and nobody knows what the future holds, what I can say is that Jackson isn't a player who leaves a club unless it's through the front door."

Gonzalo Arroyo Moreno/Getty Images

If Chelsea could help him refind the kind of form he showed at Porto—where he netted 92 times in 132 appearances, per Lustig—he could be the player they need in their attempts to return to the top of English football.

But Atleti would surely attempt to include Costa in any deal for 29-year-old Martinez, and the Blues would do well to keep hold of the Spaniard.

What Costa and Chelsea need is greater depth in the strike department. Currently Loic Remy and the out-of-form Radamel Falcao are the only like-for-like back-ups, and thus simply swapping Costa for Martinez would solve very little.