The club's training ground at Cobham, Surrey, was sealed off after a member of staff opened the package on Tuesday. A note addressed to Grant claimed the powder was lethal.

A police source confirmed that the note to Grant, 52, included the words: "You are a back-stabbing Jewish b******. When you open this letter you will die a very slow and painful death."

Death threats of a sexual nature were also made to Grant's wife, Tzofit, a well-known television personality in the couple's native Israel.

A spokesman for Surrey Police said: "We were called to Chelsea's training ground at Cobham at 12.15pm yesterday after they received a suspicious package.

"A white powder contained within the package was analysed by specialists from Surrey Fire Service and was determined to be a harmless substance.

"Detectives are continuing investigations to identify the source of the package."

At the time Grant and Chelsea were in Athens ahead of Tuesday night's Champions League 0-0 draw with Olympiacos.

Chelsea said in a statement on Wednesday: "A suspect package was sent to Chelsea's training ground yesterday. The required procedure for dealing with such matters was immediately activated and the police and other services were called to handle the situation.

"A harmless substance was discovered. The matter is still being investigated."