6 players so far
The Sweedish striker Henrick Larson played many years for Celtic in Scotland, but played only a year for Manchester United.
There are 11 players on the field, and there are 7 subs on the Chelsea side
Juan Sebastien Veron
I remember only one Arjen Robben, from Chelsea to real Madrid , he now plays at Bayern Munich.
as per my knowldge i only see 3 player have played for Celtic and Southampton here is the list of three. Victor Wanyama Virgil van Dijk Fraser Forster