The bad news is that even without being fully fit he has scored seven goals in his opening four matches for his new club since his 32 million pounds transfer from Atletico Madrid.
               
Schalke will have plenty to fear if, as expected, he plays against them at Stamford Bridge.
               
Those goals, which included a hat-trick in Chelsea's 4-2 win over previously unbeaten Swansea City on Saturday, have helped preserve Chelsea's perfect start to the season, in contrast to winless Schalke's start in the Bundesliga.
               
Chelsea are top of the Premier League with a maximum 12 points while Schalke are languishing near the foot of the German table with one point from their first three matches.
               
They know what to expect from Chelsea, too, after losing to them 3-0 both home and away in last season's Champions League group stage, and on current early season form Chelsea look capable of beating them again by at least that margin.
               
After another impressive performance on Saturday, Costa, the first player since 1992 to score in his first four Premier League games, said despite his great start he had not yet settled down to life in London, but was settling in well at the club.
               
"I have not yet been out in London, but I am trying to get to know it and bit by bit adapt to London," the Brazil-born naturalised Spain international said.
               
"To have an old team mate (Filipe Luis) here is very important. Ramires, Willian, Oscar, Cesc Fabregas and Cesar Azpilicueta have all helped me a lot. I am very happy,” he added.
               
Fabregas, who joined Chelsea from Barcelona in the summer, has also made an excellent start at Stamford Bridge, with assists in every game he has played so far.
 
While Chelsea are on the crest of a wave, Schalke, who finished third in the Budesliga last season, are in a crisis.
               
The royal blues were crushed 4-1 by Borussia Moenchengladbach on Saturday and are two off the bottom with just one point and a goal difference of minus four. That point came from a 1-1 draw with champions Bayern Munich.
               
Schalke, who also lost 2-1 to third-tier Dynamo Dresden in the opening round of the German Cup a month ago, sought more consistency this season after last season's rollercoaster ride.
               
But coach Jens Keller has yet to get the most out of a talented squad, with Kevin-Prince Boateng sluggish in midfield and attacking midfielder Julian Draxler and Dutch international striker Klaas-Jan Huntelaar playing below par.
               
Keller's cause has not been helped by a thigh injury to defender Felipe Santana, while other injured squad players are also out and restricting his options.
               
Forward Sidney Sam, who has arrived from Bayer Leverkusen,   has not yet added the pace to their game they expected, and their defence has let in seven goals in their three league games.
               
With Chelsea awaiting in the Champions League, Keller knows time is running out for him to start delivering.
               
"There is no point in talking much about it now," he said after Saturday's defeat at Gladbach.
               
"We will now work hard in the coming days, lick our wounds and pick ourselves up. We want to present ourselves well at Chelsea,” he added.

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