The good news for Schalke 04`s defenders as they prepare to face Chelsea in their opening Champions League Group G match on Wednesday is that striker Diego Costa is nursing a slight hamstring injury.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, reports Reuters. 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.