The Premier League club said they had the option to make the transfer permanent.
"We expect him to be out until mid-April, end of April, May, even next season I don't know, " Jose Mourinho explained according to UK Sun.
Fernandes will provide vital cover in midfield following a three-month lay-off for Moussa Sissoko, who has had knee surgery. "All of us as players want to stay near the best, so it's fantastic to work with him". "But I can also say that he is helping us in matches that he is playing with us". "I've never seen anything like this - it's unbelievable".
Chelsea FC are now preparing for their home Premier League clash against Burnley at Stamford Bridge on Saturday afternoon.
It looked like being a long night for Boro in their FA Cup third-round replay after early goals were gifted to Jose Mourinho's Spurs - with Giovani Lo Celso and Erik Lamela being the beneficiaries.
Back in 2009, Benfica agreed to give youth team SC Frielas €250 (which amounts to £215) along with 25 footballs in order to beat Sporting Lisbon to the signature of Gedson Fernandes.
The Portuguese international's imminent arrival could open the door for Christian Eriksen to secure a move to Italy with reports suggesting he's in talks with Inter Milan after refusing to sign a new contract at Spurs.