Ronaldinho believes Chelsea will live to regret selling striker Eidur Gudjohnsen to Barcelona.
Gudjohnsen ended a six-year stay at Stamford Bridge during the summer when he was allowed to join Barcelona for £8million.
The Iceland international has been quick to make his mark at the Nou Camp, scoring a spectacular late goal as Barcelona opened their La Liga season with a 3-2 win at Celta Vigo.
He will be back in west London next month for Barcelona's Champions League clash with Chelsea and Ronaldinho is confident Gudjohnsen will return to haunt his old team-mates.
'He is a great player and he showed that when he played in England,' said the Brazilian superstar.
'He has already shown with Barcelona that he is a very skilful guy. He will prove to be very important for us this season and he will also help us against Chelsea.'
There is little love lost between Barcelona and Chelsea, two of Europe's leading clubs, who meet in the Champions League for the third successive season.
Barcelona prevailed last year en route to winning the title and Ronaldinho is the relishing the chance to test himself against Jose Mourinho's Premiership champions once again.
'I never get tired of playing Chelsea. All the top players and the top teams want to play against the best teams,' he said.
'Chelsea are one of the biggest clubs in the world. It is always a thrill to play against them and I am happy we are meeting at this stage in the Champions League.'