Manu re-injuring the ankle at the Olympics, I believe, is a blessing in disguise.
Had he not gone to the Olympics there is no doubt he would tried to play here at the beginning of the season even if his ankle was still not 100%. From what I know of Manu, he would have pushed on and kept playing, even if was bothering him, for as long as he could physically stand it.
Then, at some point in the regular season that ankle would have given again, reguiring surgery, and we'd have been without Manu for the stretch run, perhaps, and with a still-recovering Manu for the post season. Or perhaps Manu would have put off surgery because of his compe iveness until after the season was over, playing at 70% trying to compensate for his injury.
This way Manu can sit out the first part of the season when teams aren't trying all that hard anyway and properly rehab after his surgery. The Spurs can determine who on their team they can count on, other than Manu, to step up and win games, and then we'll have Manu healthy (hopefully!) for the post season run.