It really must have been the knee (I was worried he was going to have a Tim situation with that knee affecting his offensive performance, jumpshots etc.) but he's come back playing well. I think Pop is going to have to manage his minutes carefully (Manu too. I know Pop didn't want to play him more than 20 minutes on a B2B.)
With the Spurs bench being so young and rooks (I mean Laprovittola, Murray?) I don't know how Pop will manage it, but he's going to have to keep them both rested and healthy through the season.