(AP) - Don't know what Willie Nelson was taking or doing for his sore shoulder - but he sure has gotten better in a hurry.

A day ago, he was supposed to be laid up a week because of his shoulder - and among the gigs he would miss was a music festival tomorrow in Nashville. But now comes word that Nelson will do Zac Brown Band's Southern Ground Music & Food Festival after all.

Warren Haynes will sit in with Nelson and his band for part of the performance. Just as there was no explanation about the details of the shoulder injury, there was no explanation for how Nelson was able to get back to work so soon. He apparently isn't 100 percent though. He will still miss three other dates he was to do - but will make those up.