Last month, Chelsea announced that Diego Costa will rejoin Atletico Madrid at the start of the upcoming January transfer window.

The Brazil-born Spain international fired the Blues to the Premier League title last season with 22 goals, but over the summer, Antonio Conte told him he was no longer in his plans.

Since then, Costa has been up to all sorts, including lots of partying in Brazil, but it looks like the controversial forward is finally stepping up his fitness regime.

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With the likes of Antoine Griezmann, Kevin Gameiro and Angel Correa at Atletico, it's no guarantee that the ex-Chelsea man will back into the club's starting XI.

However, there is one thing another Atleti star is doing to help Costa get ready for match action, and he happens to be a former Chelsea player.

Ex-Chelsea star helping Costa get match-fit

No, it's not Filipe Luis. Former Chelsea striker and Atletico Madrid legend Fernando Torres, yet to score this term, is helping his new teammate regain power and full fitness.

Atletico have been putting Costa through his paces by setting up one-one training sessions for him with fitness coach Oscar Ortega.

However, Torres has gone one step further by allowing Costa to work out and do some boxing at his own personal gym, called NineFitness.

Check out the images of Costa in the ring below, via The Mirror:

The 33-year-old Torres, who owns the NineFitness franchise, recently posted a video on Instagram of Costa sparing with a trainer, which you can see below.

The caption read: "The best trainer in NineFitness, Diego Costa works out in our club with Jesus Garcia Pola."

Atleti's transfer ban means Costa is unable to feature until January, but, judging by these images, the striker will make a big impact when he eventually makes his anticipated return.

The 29-year-old's second debut for Diego Simeone's men, currently fourth in La Liga, could come on January 7 when they take on neighbours and rivals Getafe.

What do YOU make of Costa working on his fitness in Torres' gym? How good will he be when he returns to action? Leave YOUR opinion in the comments box below!