Diego Costa
Diego Costa has scored seven goals in just four games.Getty

Chelsea's new signing Diego Costa has tried to lower his goal expectations for the season despite an amazing start at Stamford Bridge.

The Spanish international striker scored a hat-trick during the 4-2 victory over Swansea on Saturday to prolong Chelsea's perfect start to their campaign after four Premier League games.

The 25-year-old forward has scored seven goals for the Blues since his £32m summer move from Atletico Madrid, having netted at least a goal in each of their Premier League games.

The striker scored 27 La Liga goals campaing for Atletico Madrid but urges caution to the fans and alerts them he may not be able to maintain this level during the whole campaign.

"I try to play in the best manner, and hopefully things will continue like this. But there will be a moment when I cannot score - that is football," Costa said, according to Standard Sport.

The new Chelsea star has already netted two more domestic league goals than Fernando Torres and Demba Ba during the whole last campaign, while only two fewer than Samuel Eto'o.

"It is different for every striker who comes here," Costa said.

"Every striker has their way of playing and their strengths and a different team behind them. That is very important. If you do not have the team behind you then you can't do things on your own. It all depends on the team. It could be because of that."

Meanwhile, manager Jose Morinho has lavished praise on Costa while admitting he's astonished about how he has managed to settle in the Premier League.

"Seven goals is a surprise. Nobody expects one player to score seven goals in four matches, and they're not penalties, it's from free play. Everybody was expecting him to succeed, to feel comfortable, to adapt to our team and to our Premier League. To score seven goals is obviously a fantastic record," the manager explained after the Swansea game.