The Blues look set to beat Premier League rivals Manchester United and Arsenal to the signing of the Portugal forward, with neither side willing to pay the €11m (£9.69m) loan fee.
Felix would provide a much-needed boost to head coach Graham Potter’s attacking options, with his side scoring just 20 goals in 17 Premier League matches this season.
Despite the transfer window only being open for just over a week, Chelsea have already been active in January, signing Benoit Badiashile, David Datro Fofana and Andrey Santos.
Potter will hope their arrivals can help to improve his team’s form, with just one win coming from their last seven matches in all competitions.
Chelsea are currently 10th in the Premier League – 10 points outside the top four – and have already been knocked out of the FA Cup and Carabao Cup.
The west London club’s only realistic remaining hope of silverware this season is in the Champions League, where they face Borussia Dortmund in the last 16 next month.
Felix has just seven LaLiga starts for Atletico this season but he was named in the starting XI for their 1-0 defeat at home to Barcelona on Sunday.
However, the LaLiga side are prepared to let Felix – who has five goals and three assists in all competitions this season – leave on loan in January because of his difficult relationship with manager Diego Simeone.
The 23-year-old joined Atletico from Benfica in a €126m (£111m) deal from Benfica in 2019.
Source: Sky Sports