The world number one had hoped to play at this week's Memorial tournament in Ohio but opted out of the event in the hope of being fully match fit for the US Open.
"The knee is doing better," he said. "The rehab is working.
"It gets really old riding that bike, man. But everything is on schedule. Just trying to get this thing (the knee) organised for the (US) Open. Right on schedule for that.
"It has been slow. It has been boring, but the leg is starting to gain some strength.
"It's hard to be patient. You know, I am not a patient kind of guy when it comes to that.
"I always want to go all out. Sometimes it is hard for me not to do that, but I have got to be smart about it. And I've done that."



