The 21-year-old Egypt international has yet to agree personal terms, but he is expected to agree a move to Stamford Bridge assuming that he passes a medical and is granted a work permit.
Salah had been long linked with Liverpool and was expected to be their big January capture, but Chelsea made a late move to secure the player in order to fill the hole about to be left by the outgoing Juan Mata and Kevin de Bruyne.
Dubbted the 'Egyptian Messi', Salah had represented his country at every level by the age of 19 catching the attention of several clubs during the London Olympics in 2012 where he scored three goals in four appearances.
He joined Basel as a replacement for Xherdan Shaqiri of Bayern Munich, and scored in his second appearance for his new club in the Swiss League against Lausanne.
He scored in against Spurs in their win over Chelsea's London rival in last season's Europa League quarter-finals while he also netted against Chelsea in their 5-2 loss in the semi-finals.
He was touted for a move to Chelsea during the close season, but it seems their interest has been revived after Salah netted in a 2-1 win in the Champions League in September before netting the winner home soil against Jose Mourinho's men in November.
He has made 24 appearances for Basel this season, scoring six times.
The morning papers revealed that the extra interest in Salah had seen his asking price jump from £12 million to £16 million, though Chelsea have not confirmed how much they will pay.
He becomes Chelsea's third signing of the winter transfer window, following Bertrand Traore and Nemanja Matic.
Liverpool were tracking the talented forward for some time, a fact manager Brendan Rodgers confirmed this week in a press conference.
"We’ve looked at a number of players, but Salah is a talented player, but we’ll see what the window brings," said the former Swansea manager.
"We’re looking at several targets."
The move is reminiscent of the deal for Willian, who had already completed a medical at Tottenham before signing for Chelsea last August.
Prior to De Bruyne's departure to Wolfsburg earlier this month, Mourinho insisted there was no need for a like-for-like replacement for the Belgian, yet now Salah has come in with Mata Old Trafford-bound.
Salah is another option in the attacking midfield roles, but the pace and width he offers suggests Mourinho seems him as an alternative to Mata, rather than a direct replacement.
Mata, Chelsea's player of the year in his two seasons since joining from Valencia, has struggled to cope with Mourinho's demands for a greater work ethic, with Eden Hazard, Oscar and Willian favoured in the three attacking positions behind a lone centre forward.
Mata has completed just one of the last five games he started and last featured on New Year's Day at Southampton, where he reacted angrily to his substitution early in the second half.
Mourinho will hope Salah, who is 21, can be sculpted as he wishes and learn to play as his manager demands, like Hazard has.
Striker Fernando Torres will miss the Stoke match with a knee injury, the full extent of which may be revealed by Mourinho on Friday at his pre-match media conference.
Mourinho has repeatedly insisted Chelsea will not be purchasing a striker during the January transfer window, even after the Torres blow, and he instead promised to give Demba Ba an opportunity.
Ba has not started for the Blues since October 6 at Norwich.
The "killer" striker Mourinho craves will have to wait until the summer, with the Portuguese still an admirer of Wayne Rooney.
Manchester United rebuffed two bids for Rooney last summer, but the 28-year-old will have a year to run on his current contract at the end of this season.
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- Jose Mourinho
- Juan Mata