Avram Grant was sent a package containing a mysterious powder

A note addressed to Grant was opened by a member of staff. It was found to contain anti-Jewish insults as well as claims that the powder was lethal.

A police source said it used the words: "When you open this letter you will die a very slow and painful death."

The powder was analysed by specialists and found to be harmless, police said.

The letter also included threats to the manager's wife Tzofit, a well-known personality in 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."

The club's training ground at Cobham, Surrey was sealed off while investigations were carried out.

Detectives are continuing to try to identify the source of the package.

In a statement, Chelsea said: "The required procedure for dealing with such matters was immediately activated and the police and other services were called to handle the situation.