Tiger Woods says he is happy with the pace of his recovery from back surgery but does not know when he will play again.
The 14-time major winner has not competed since undergoing two procedures on his back in September and October last year.
The 40-year-old former world No 1 fuelled speculation about a comeback after registering for the US Open in June, before playing five holes with friend Mark O'Meara at Bluejack National Golf Club in Texas on Monday.
It was the first time he had played since surgery in October and he said he felt "a little tired but pretty good".
"I haven't set any date to when I'm playing again, which is frustrating to say," he added. "But to be honest with you, that's what I've had to do. I've had to go with that mindset.
"Would I have said that five months ago? No way. I couldn't imagine then feeling like I do right now. Keep improving. Keep getting better. Keep making progress. And I'm doing that."
Agent Mark Steinberg told ESPN on Monday that Woods' registration for the US Open at Oakmont Country Club was "simply procedural" and there was "no reason to read anything into this".
Woods also registered to play in the US Open last year before backing out.
Earlier this month he ruled himself out of the Masters at Augusta, saying that while he had begun hitting balls again, he would not be fully fit for the tournament.