* Walks off at eighth hole
* Says he has strained ligament and muscle spasm
* Plans 'long break' (Adds details, quotes, recasts)
Sept 23 (Reuters) - Jason Day downplayed any concerns over his playing future after an on-going back injury prompted the world number one to pull out of the Tour Championship during the second round in Atlanta on Friday.
Day, 28, also withdrew during the final round of his previous tournament, the BMW Championship two weeks ago.
"Jason has a strained ligament in his lower right back with muscle spasm," his management company said in a statement shortly after early departure at East Lake.