The former Arsenal midfielder will undergo a medical on Monday and sign a £50,000-a-week deal with the Blues.
Sidwell will join Chelsea on a Bosman free transfer.
Royals boss Steve Coppell will not include Sidwell in the squad for tomorrow’s trip to Blackburn.
Coppell said: “I don’t think he’ll be in the squad.
“Realistically he’s going. It’s a great opportunity for him and he’ll push on.”