He must have known payment was going to be late at least a few days ago so why not simply contact Karl and say "Look, cashflow's been a nightmare so I'm afraid your money's going to be a bit late. We will pay you but it won't be on the 6th, it'll be on (earliest possible date) instead. I'm sorrry it's been delayed but we had to pay off HMRC, BluMarble and the rest and there's just not enough left in the bank to cover you as well because there's no game that weekend so no income."
Speaking as someone who has run a business and been on the receiving end of late payments I was never overly annoyed about being paid late so long as I knew it was going to happen and when I'd actually get my money. What really annoyed me was when I didn't get paid on time and there'd been no word or warning from my debtor to tell me that was going to happen. In this day and age there's simply no excuse for not communicating with a creditor. If Ken has failed to speak to Karl on this issue (and I'm not saying that's the case because we don't know everything that's happened) then that's just plain wrong. A simple phone call or even an e-mail either to Karl or his agent wouldn't have taken long and in ensuring everyone knew where they stood this latest 'spat' on Twitter would have been avoided.
However if Ken has made that call and Karl's neglected to mention it then I think diving on Twitter and neglecting to mention that fact is poor from Karl. Since we don't know all the facts in this case it might be wise to wait and see what comes out next. One thing I will say is I find this habit of people 'washing their dirty linen in public' via Twitter to be extremely distasteful whether it's a late paid footballer or the President of the United States doing it. If you have a problem surely it's better to discuss it with the person directly rather than jumping onto Social Media in what can look like a rather childish bid to get other people worked up.