Oscar Piastri has not been able to show his true pace in Las Vegas, with the second practice session on Friday (AEDT) being cut short for "track maintenance".
Formula 1 drivers' championship leader Lando Norris finished the session on top of the time sheets with a fastest lap of 1 minute 33.602 seconds.
Two red flags came out in the final 15 minutes of the one-hour session, not allowing the drivers a proper chance to post their best times.
Reports suggested a manhole cover was feared loose on the street circuit, with race directors electing to investigate as the session was stopped for "track maintenance".
Oscar Piastri, who enters this weekend 24 points adrift of Norris in the drivers' championship, never had an opportunity to produce a fast lap on the soft tyres, finishing the session 14th fastest.
McLaren has struggled in the two previous editions of the Las Vegas Grand Prix, with a best result of sixth (Norris) and seventh (Piastri) last year.
McLaren used different rear wings for Piastri and Norris, with the Australian running with a skinner wing as the team tried to find the optimum set-up for the tricky Las Vegas track.
"We'll look through the data tonight and come to a conclusion, but yeah, we are running two different configurations," McLaren chief executive Zak Brown told Sky Sports.
Despite the drivers not being able to show their true potential, McLaren appeared to have improved compared to the first practice earlier on Friday.
Ferrari's Charles Leclerc was fastest after the first session, ahead of Williams driver Carlos Sainz, then the Red Bull duo of Yuki Tsunoda and Max Verstappen.
The final practice session and qualifying will be held on Saturday, AEDT.
ABC Sport will have a live blog of the Formula 1 Las Vegas Grand Prix on Sunday, November 23, with the race beginning at 3pm AEDT.
