After cooling interest in Olivier Giroud and Kelechi Iheanacho, West Ham have also reportedly made Hernandez a priority target ahead of next season.
The 22-year old revealed it was the successful careers of Claude Makelele and Didier Drogba, two Chelsea legends, who had the biggest influence on his decision to join Chelsea.
The former Manchester United striker Hernandez is said to be demanding wages of £140,000.
Playing for a big club like Chelsea is already good enough incentive for most players.
Costa was well-suited to the English game, and his 52 Premier League goals came from just 89 appearances, leaving him with one of the best goals-per-game ratios in the top flight over the last three seasons.
"Now the work starts for all of us together to progress". As per Sky Sports, the Frenchman is keen to stay with the Premier League champions, but acknowledges that his opportunities in the side would be few and far between. He haspreviously played for France alongside his teammate Kante, who has been recognised as the best central midfielder in England, winning a multitude of awards last season.
The £40 million fee for Bakayoko is the highest Chelsea has paid for a midfielder.
"I am now looking forward to evolving under this fantastic coach and alongside so many great team mates".