Alonso was taken to hospital for scans after the race at Yas Marina two weeks ago, in which he tripped a 25g force alarm in his Ferrari after clattering over the run-off while racing side-by-side with Jean-Eric Vergne's Toro Rosso.
Alonso revealed his back has been giving him some pain between sessions this weekend, but he says the issue has not troubled him unduly.
"My back is not a problem," he said after qualifying sixth for the US GP.
"After Abu Dhabi I was fine for three or four hours after the race, but when I did the medical check they found some lack of sensitivity in my left arm and leg and they were a little bit worried.
"I had a lot of headaches after, because a nerve was compressed and there was not enough blood pressure in my head. The nights were very difficult but slowly the inflammation came down.
"I had a little bit of pain yesterday and this morning when I woke up, but when you are in the car you forget it."
Ferrari struggled to build sufficient tyre temperature in a blustery qualifying session at Austin and Alonso's team-mate Felipe Massa wound up only 15th on the grid, but the Spaniard is confident the Scuderia will be more competitive in the race.
"It was a tricky qualifying, but I think we have better race pace and I expect to have a little bit more of a competitive package [tomorrow]," he added.
"Starting sixth we will have to survive the start and the first corner and then I think we can fight.
"I've had more impossible podiums than this in the past, but I don't think it's fair to think of the podium because we are starting sixth."
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