US GP: Button worried about first-lap chaos after poor qualifying

An apparent throttle issue forced the McLaren to return to its garage near the end of Q2 at Austin.

Having recently been eliminated in first-lap chaos in Korea following a troubled qualifying session, Button admitted the chances of a shunt at Austin's distinctive first corner were playing on his mind.

"It's going to be a long day. I don't think it's that easy to overtake here. I think it will still be a fun afternoon," he said.

"But Turn 1 is the tricky bit, starting from the middle of the pack.

"I was there a couple of races ago and it didn't end well for me so we'll see what we can do.

"Hopefully we can put on a great show for the American fans here."

The Briton said it was too soon to identify what had caused his McLaren to slow.

"I don't really know what the issue is. We're looking at the data," he said.

"But top speed was probably about 100 km/h, so we had a problem."

Button was relieved that he had at least managed to get a reasonably competitive Q2 time in before the issue struck.

"I did get one lap in and luckily enough I pushed on that lap otherwise I would be starting 17th," he acknowledged.

The problem came amid a run of technical glitches for McLaren in recent races. The team remains adamant that the failures are unrelated rather than evidence of fundamental problems, and Button said the latest issue would definitely hurt.

"It's something that McLaren doesn't take lightly, we'll definitely feel it, as they do every reliability issue," he said.

"We'll make sure this doesn't happen again."