The Labour-supporting Manchester United manager gave £1 more than the SNP's desired limit to the pro-Union campaign as a tongue-in-cheek "symbolic gesture".
The donation followed calls from the SNP for both sides in the early phase of the campaign to accept a voluntary limit of £500 on donations from voters outside Scotland.
Ferguson said: "Scots living outside Scotland but inside the UK might not have a vote in the referendum, but have a voice and we care deeply about our country. I played for Scotland and managed the Scotland team. No-one should question my Scottishness just because I live south of the Border."
Meanwhile, it has emerged that ministers could face a legal challenge if they insist on lowering the spending limits for the independence referendum, contrary to proposals from the Electoral Commission.
The pro-Union No campaign warned last night that the proposed limit would "stifle debate".
Better Together raised the prospect of legal action as it published a scathing submission to the Electoral Commission on how the final leg of the campaign in 2014 should be financed.