The Portuguese was sacked by owner Roman Abramovich after the Blues' 1-0 away defeat to West Brom on Saturday, a result which saw them slip out of the top four.
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However, Vialli, who won the FA Cup and European Cup Winners Cup during his time as boss at Stamford Bridge between 1998-2000, believes a complete change of staff would have been more appropriate.
He said on Twitter: "Personally I don't like it at all when the manager gets sacked and his assistant stays in charge. I thought they were a partnership.
"Having said that, good luck to RDM [Di Matteo]! Hope he can steady the ship."
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