Silvestre is a close friend of Ousmane Dabo, who was allegedly assaulted by his former Manchester City team-mate Barton in May.
Barton moved to Newcastle this summer, and France defender Silvestre admitted that was the reason he could not bring himself to move to Tyneside.
He said: "It was a good contract and a fine opportunity, but money is not the only thing in life. I could not sign for Newcastle out of respect for Ousmane Dabo."
Barton, who is currently out with a fractured metatarsal, denies a charge of causing Dabo actual bodily harm. He faces trial on October 4.