Capello's youngest son, 36-year-old Pierfilippo, is tying the knot with his partner, Tiziana, in Milan.
It was originally intended that England's friendly against world and European champions Spain would be played on Friday evening.
But the match was put back to Saturday as Barcelona - who provide eight of the Spanish squad - are in action on Wednesday evening against L'Hospitalet in the Copa del Rey.
Capello's wife, Laura, will be attending the wedding ceremony.
The clash for Capello became apparent after England's Euro 2012 qualifier with Montenegro in Podgorica last month.
England host another international friendly against Sweden on Tuesday and Capello has no plans at present to return to Italy in between the two games.
England's players will be given time to relax on Sunday but will have to report back to the team hotel in Hertfordshire in the evening.
All 25 members of the squad are expected to meet up during the latter part of Wednesday before training for the first time on Saturday.
However, major injury doubts continue to surround Everton centre-back Phil Jagielka.
He has a hairline fracture of his toe which will be assessed overnight by England's medical staff.
Speaking to The Independent, Pierfilippo said of his father missing the wedding: "It is not a problem, absolutely not. He is a football manager first; he has been that ever since I was a child and sometimes being a football manager can make strange demands on your time. You just have to accept that.
"We will all toast him sitting there on the bench at Wembley and look forward to him coming to join us for the celebrations after the games."