Fernando Alonso is in danger of failing to make the grid for the Indianapolis 500 after setting the 31st fastest time on the first day of qualifying.
The two-time Formula 1 world champion faces a shootout on Sunday with five other drivers for the final three places on the 33-car grid.
If it rains as forecast, the shootout will be when weather allows next week.
Alonso had five attempts at locking in a place in the top 30 on the grid but the McLaren car was not fast enough.
"We didn't have the speed," said Alonso, who managed a fastest average over his four-lap run of 227.224mph.
"We are where we deserve today and hopefully tomorrow we will have another chance. If we do not take it, it is because we do not deserve to be in the race.
"The whole week, the speed is not really there in the car. We will not find it in one night. We will try to do a good clean run and hopefully that will put us in the top three positions."
Fastest of all was American Spencer Pigot, with a speed of 230.083mph, ahead of Australian Will Power. Briton Pippa Mann just made it into the race, one place ahead of Alonso in 30th position.
Of the other British drivers, Jack Harvey qualified 25th, immediately ahead of rookies Jordan King and Ben Hanley, all three of whom will start in those positions.
Former F1 driver Max Chilton was 35th fastest and will be one of the drivers competing with Alonso for the final spots on the grid.
Alonso now faces the difficult experience of what is known at Indy as 'bump day', when drivers take turns to try to knock each other out of the race.
After the final three positions are defined, the fastest nine drivers from Saturday will compete for pole positions and the rest of the front three rows of the grid.
If it rains, the so-called 'fast nine' shootout will not happen and the drivers will line up for next Sunday's race in the order they qualified on Saturday.
It was a chastening experience for Alonso and McLaren, who decided to set up their own team for his second attempt at winning Indy, after he left F1 last year to concentrate on his ambition to win motorsport's unofficial 'triple crown', of Indy, Le Mans and the Monaco Grand Prix.
Alonso won Le Mans last year and has twice won Monaco. Some consider the F1 aspect of the triple crown to be the world title, but as the Spaniard has won both, it is academic in his case. Only Graham Hill has ever won all three races.
He drove a McLaren-branded car run by the leading Andretti Autosports team on his debut at the Indy 500 in 2017, qualifying fifth, leading 27 laps and running competitively until his engine failed in the closing stages.
Alonso and McLaren have had a difficult week running up to qualifying at one of the world's most demanding tracks, where average lap speeds are 230mph and mistakes are punished in the most brutal fashion.
The Spaniard lost the vast majority of the first day of practice on Tuesday with an electrical issue, crashed on the second and did not run at all on the third, as McLaren struggled to build a new car, partly as a result of discovering an engine problem.
Alonso's only trouble-free day before qualifying was Friday, but McLaren effectively had to cram an entire week's preparation into that one day.
There will be questions as to whether McLaren undertook adequate preparation for their assault on Indy on their return as a self-run team for the first time since the 1970s.
Run by former Force India F1 deputy team principal Bob Fernley, McLaren's Indy team scheduled only one test day before running started in preparation for the 500.
McLaren spent a day at Texas Speedway in the second week of April, on which problems restricted running, before the official first test day at Indy on 25 April.
On their first day at the historic track, which first hosted the Indy 500 in 1911, Alonso was able to do only 29 laps as a result of electronics problems.
This week's practice has seen a series of issues for McLaren that left Alonso and the team badly under-prepared for qualifying.
Alonso completed just 50 laps of the 2.5-mile 'super-speedway' on the first day on Tuesday as a result of problems the team traced to a wiring loom, and he was 32nd fastest.
On Wednesday, Alonso had completed 46 laps before crashing at Turn Three, losing the front end and understeering into the barriers.
McLaren planned to be out first thing on Thursday for a full day, but repairing the car took longer than expected, and when they discovered the engine had been damaged as well the session was a write-off.