Chelsea have completed a £15m deal to sign Nicolas Anelka from Bolton.
The French striker, 28, has signed a three-and-a-half year deal and could figure in Saturday's game with Spurs.
Bolton had rejected a £12m bid from the Stamford Bridge outfit, who are short of forwards because of injuries and Africa Cup of Nations call-ups.
"I want to tell the Chelsea fans that I see this as a great opportunity and an honour and I will not disappoint them," Anelka told the Chelsea website.
"Chelsea is the team I really wanted to join and I hope this will be the last club that I play for.
"I am really looking forward to working with Avram (Grant) and Chelsea's style of football really suits my game."
With Didier Drogba and Salomon Kalou away on national duty, and Andriy Shevchenko injured, Chelsea boss Avram Grant was running out of options to boost his squad's artillery.
Shevchenko and Claudio Pizzaro, their other senior forward, have scored just five Premier League goals between them this season.
"It's not a secret that I was looking for one more striker, and Anelka has pace, is a good finisher and is scoring a lot of goals," said Grant.
"But he also provides assists and can play in any system and with any other good players beside him."
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Bolton manager Gary Megson said: "We wanted to keep Nic but once it became obvious that he saw his future away from the club the idea was then to get as much money as we could for him.
"We will be looking to add to the squad to improve our league position.
"If there's a centre forward available he'll have to be a hard-working centre forward to get into the team ahead of Kevin Davies."
Anelka, who has scored 11 goals in 22 games this term, had been linked with a move Chelsea despite signing a new four-year deal with Bolton last August.
He has made no secret of his desire to play in the Champions League and is still eligible for this season's competition.
Anelka joined Bolton in 2006 from Turkish club Fenerbahce for a club record £8m.
He has also played for Arsenal, Liverpool and Manchester City in the Premier League and won the Champions League while at Real Madrid.
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