The Premier League champions signed Athletic Bilbao left back Asier del Horno for $14.50 million on a three-year contract.
Costa, the Premier League's leading scorer with 14 goals, will miss Saturday's game following a disagreement with Chelsea manager Antonio Conte and a club fitness coach Julio Tous, the reports say.
Chelsea reacted angrily on Friday to newspaper reports that Carlo Ancelotti was set to replace manager Antonio Conte and that former coach Steve Holland has received texts from unhappy players who say they are missing him.
Chelsea, who won the League Cup in February, have 88 points and cannot be caught by 2004 champions Arsenal.
The English Premier League matches are on. Are you cheering for Chelsea? Or Manchester United?
Chelsea's Ivory Coast striker Didier Drogba has signed a new three-year contract, the Premier League club said on Wednesday.
The three Premier League and three La Liga clubs in the last eight avoided each other, with Manchester City up against Atletico Madrid and Liverpool to face Portuguese side Benfica.
Chelsea named former Napoli boss Maurizio Sarri as the new head coach on a three-year term on Saturday, a day after parting ways with another Italian manager Antonio Conte.
If reports are to be believed, it is a video posted online that has got the Portuguese's goat. According to the European press, Canal Plus, a French TV channel put up a video where Mourinho has questioned the quality of strikers in his Chelsea squad.
The Portugal defender signed a three-year contract for around 30 million euros.
Chelsea extended their impressive turnaround under new coach Thomas Tuchel with a 2-0 home win over in-form Everton on Monday as Kai Havertz played a key role in both goals on his return to the starting 11.
Chelsea have signed Germany's highly-rated attacking midfielder Kai Havertz from Bundesliga side Bayer Leverkusen on a five-year contract, the Premier League club announced on Friday.
The club spokesman said no immediate announcement would be made on Ranieri's successor, but added the club expected to say something within the next 48 hours.
Conte won the Premier League in his first year at Chelsea but his future is unclear after they finished fifth last season and failed to qualify for the Champions League.
Jose Mourinho was purring like a cat that had devoured the leftovers from Christmas dinner but it did not stop him showing his professional claws after his Chelsea side eased past West Ham United 2-0 on Friday.
UEFA announces UCL final hosts for next four seasons.
An 85th minute goal from a free kick by Ireland winger Damien Duff gave Chelsea a 2-1 victory over Manchester United.
Striker Didier Drogba scored on his debut as Chelsea won 3-0 in the Champions World Series.
The Chelsea captain signed a revised five-year contract to stay with the English Premier League club until 2009.
Chelsea's 3-0 win over Middlesbrough on Monday moved them seven points clear at the top with three games left and a win at West Brom will make them champions.
Having spent much of his time at Chelsea operating in Eden Hazard's shadow, Willian has emerged as a leading light in the team ahead of their Champions League showdown with Barcelona.
The French midfielder's move to London went through as planned, despite a disagreement over the player's cut of the transfer fee.
Chelsea got their Premier League campaign on track after 20-year-old right back Reece James helped them to a 3-1 win at Brighton & Hove Albion with a spectacular goal on Monday.
Chelsea manager Maurizio Sarri is uncertain if Kepa Arrizabalaga will start Wednesday's English Premier League match against Tottenham Hotspur after the goalkeeper's refusal to be substituted in their League Cup final defeat by Manchester City.
Manager Guus Hiddink dismissed speculation that Eden Hazard will leave English Premier League champions Chelsea, insisting that the winger is content to stay at Stamford Bridge.
Lampard was handed a three-year contract having left second tier Derby County.
Images from Wednesday's action in the Champions League.
Holders Chelsea made light of their off-pitch problems to reach the Champions League quarter-finals by beating Lille 2-1 away on Wednesday to complete a 4-1 aggregate victory.
Chelsea defender Antonio Rudiger says "racism has won" and that he had been made a "scapegoat" after Tottenham Hotspur and London police said they found no evidence to back his allegation he was abused during the English Premier League match in December. Rudiger was involved in an incident in which Tottenham's Son Heung-min was shown a red card and indicated shortly afterwards that he had been the victim of a monkey gesture from the home section of the crowd.
Chelsea have re-signed midfielder Nemanja Matic from Benfica, three years after selling him to the Portuguese side, the Premier League club said on Wednesday.
Liverpool's Mohamed Salah ended his Premier League goal drought in style by scoring twice as the champions raided the capital again to crush West Ham United 3-1 on Sunday.
Chelsea have followed up the dismissal of manager Avram Grant by sacking his assistant Henk ten Cate, the Premier League club said on their Web site on Thursday. Ten Cate left his job as coach of Ajax Amsterdam to join Chelsea in October 2007 as assistant to Grant.
Chelsea manager Frank Lampard was delighted with the discipline of his team, who ended United's 19-game unbeaten run.
Terry is clearly delighted to have been reunited since with Portuguese Jose Mourinho, under whose guidance he has won three of the four Premier League winners' medals he owns.
A summary of Saturday's action in the Premier League.
Antonio Conte said his Chelsea players were fatigued after only 30 minutes of their 1-0 loss to Manchester City.
Porto defender Jose Bosingwa has agreed a three-year deal with Chelsea and will join the Premier League runners-up after Euro 2008, the club said on Monday. "Jose Bosingwa has agreed terms with Chelsea Football Club. He has agreed a three-year contract," said a statement on the club's Web site (www.chelseafc.com).
