Spanish Euro and World Cup winning striker Fernando Torres has pledged to try his heart out to regain the form that saw him become one of the most feared marksmen in world football.

The 29-year-old – capped over 100 times by his country – has failed to replicate the form for Chelsea that earned him a STG50 million ($A73.51 million) move in January 2011 from Liverpool.

However, a brace against Russian side Rubin Kazan on Thursday in their Europa League quarter-final, first leg clash took him to 18 goals for the season and gave him hope that he is on the right track.

I want to do the things I used to do all my life,” he told the Daily Mail.

“I did them at Atletico Madrid, I did them at Liverpool and I am not doing them at Chelsea. I am working on it. If I knew the reason, I would fix it in one minute. But the only way to fix these things is to work at it.

“I am training every day and I will never, ever give up.”

Torres, who scored 65 goals for Liverpool in 91 league starts, said that he was enjoying being at Chelsea and hoped he could propel them to the FA Cup and Europa League trophies, and hence salvage something from a generally disappointing season.

“I am happy here,” said Torres, who has had to play a secondary role first to Didier Drogba and now Demba Ba since he moved from Newcastle in the January transfer window.

“I am enjoying London and happy at this club.

“I know my statistics at Chelsea have not been the same as in other years in my career. But I am fighting to get back to those statistics and I will never, ever give up.

“I will try my heart out for this club. There are too many things I have to give back to these people and I want to show my thanks to them.

“Hopefully this season we can give them two more trophies and next season we can fight again for the biggest ones, the Champions League and the Premier League.

“I am getting better but I’m still not at the level I want.”

Torres will have to wait to see whether his double was enough to earn him a start in Sunday’s Premier League home match against relegation-threatened Sunderland.