Sidwell left Reading after refusing a new contract and Steve Coppell has confirmed that the 24-year-old is no longer at the club.
"Steve has gone. I know exactly where he has gone to but I'm not allowed to say," said Coppell.
Also heading for the Bridge is surprise package Mark Viduka.
Aussie striker Viduka, 31, said on Sunday he had a lot of thinking to do and was not very good at making decisions.
However the lure of a tilt at the Premiership next season as well as Champions League football could be too good an oppertunity to turn down.
The Middlesbrough striker is expected to leave the Riverside atb the end of June.
Chelsea boss Jose Mourinho hinted at the changes coming to Stamford Bridge.
he said: "It is obvious that we need a couple of players, two or three players. That's the nature of a team like us which is trying to improve.
"We need a central defender, a midfield player to make the group stronger, especially a group that will lose Jon Obi Mikel and Michael Essien at the same time for the African Cup, and we need a striker."