Earlier this year, President Barack Obama ordered 21,000 more troops to Afghanistan, which will bring the total number of U.S. forces there to 68,000 by the end of the year.
McChrystal is expected to ask for more troops soon, but would not elaborate on numbers Friday.
"My position here is a little bit like a mechanic. We've got a situation with a vehicle and I've been asked to look at it and tell the owner what the situation is and what it will cost to make the vehicle run correctly and I will provide that," he said.
"Now I understand that the vehicle owner then has to make a decision on what the car is worth, how much longer he intends to drive it," he added. "Whether he wants it to look good or just run."
He should have traded it in during the Cash for Clunkers program.