Red Bull team principal Christian Horner has refused to confirm whether Sergio Perez will finish the season with the team amid doubts over his future.
Perez is contracted to Red Bull into 2025 but there have been growing concerns over his performances and results in recent months.
The Mexican began the season with four podiums in five Grands Prix, but has not finished higher than sixth since the Miami Grand Prix in May.
The Mexico City Grand Prix - Perez's home race - was a fresh low, after the six-time race winner had started in 18th place.
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He was given a five-second time penalty for a false start before later colliding with RB's Liam Lawson, which caused significant sidepod and underfloor damage and ended any chance of the 34-year-old finishing in the points.
Perez finished the race in 17th and last - the second time he has crossed the chequered flag in that position this season.
What is particularly worrying for Red Bull is that, unlike last year, they are locked in a battle with McLaren and Ferrari over the Constructors' Championship - and it is one they now look extremely likely to lose.
While Perez's team-mate Max Verstappen himself hasn't won a race since the Spanish Grand Prix, the championship leader has been consistently quicker than the Mexican and has still regularly finished in the top five.
After the race, Red Bull team principal Horner was asked about Perez's future - and he struck a notably different tone in his answer compared with recent months, where he had backed Perez to improve.
He told The Associated Press: "Look, it's a performance-based business.
"As a team, we need to have both cars scoring points. That's the nature of Formula 1.
"From a team's perspective, we're working with him as hard as we can to try and support him.
"I think we've done everything that we can to support Checo, and we'll continue to do so in Brazil next weekend. There comes a point in time that you can only do so much [as a team].
"There comes a point in time that difficult decisions have to be made. We're now third in the Constructors' Championship. Our determination is to try and get back into a winning position, but it's going to be a tall order over these next four races."
Among the favourites to replace Perez are the RB pair of Liam Lawson and Yuki Tsunoda - though Horner admitted they 'didn't have a great day either' in Mexico.
Both drivers will test the Red Bull in Abu Dhabi following the end of the season.
Tsunoda has far more experience in F1 than Lawson - he has been driving full-time in the sport for four seasons, compared to Lawson's half season in 2023 plus the last two races - but Red Bull have resisted calls to call up the Japanese driver in the past.
While Tsunoda started the season consistently strongly, he has endured a tougher time of late, with two mechanical failures causing him to retire from the Italian and Azerbaijan Grands Prix.
In Mexico, he suffered two crashes over the race weekend, including a lap one racing incident with Alex Albon that caused him to retire again.
Lawson, meanwhile, finished an impressive ninth on his return to the RB team in Austin after replacing Daniel Ricciardo. But he finished 16th in Mexico after incidents with Perez and Franco Colapinto.
Topics: Formula 1, Red Bull Racing
Ryan Smart