McLaren admit they have plenty of work to do after enduring a difficult start to their Mexican Grand Prix weekend.
Daniel Ricciardo and Lando Norris ended up in 14th and 15th respectively on the Free Practice 1 timesheets, whilst Free Practice 2 brought further issues.
Norris recorded the 12th fastest time, but Ricciardo spent most of the session in the garage due to a gearbox issue on his MCL35M. He finished the hour in P15.
Ricciardo says this left him unable to achieve a great deal during Friday's running, and as such the team have to act fast to make improvements ahead of Saturday.
"Unfortunately, we didn't really get much done this afternoon," the Australian explained. "We had an issue in FP2, so we only completed the Hard run.
"These things happen, and we'll just have to get into it tomorrow. We don't have any time to waste so we'll get amongst it.
"We've got a few challenges ahead but we'll be alright. We got enough information from Lando today to be able to pick it up tomorrow."
Confident of improvements
Meanwhile, Norris also acknowledged that it had not been a smooth start to the weekend for the Woking-based squad, but remains hopeful that they can make progress.
"A difficult day as we struggled with the balance and the overall grip level," Norris said.
"I think we've found some positives between FP1 and FP2. We can be confident we're going to make some improvements into tomorrow and find a bit more lap time.
"It's not easy, so we'll work hard overnight and see what we can find."
McLaren remain in a closely-fought battle with Ferrari for third place in the Constructors' Championship, and the team's Executive Racing Director, Andrea Stella, knows how important it is that they try to stay on a level with their competitors.
"Today's practice sessions showed us what we expected to see here in Mexico City," Stella added.
"The altitude pushes us to tune several aspects of our setup to cope with the cooling requirements and low downforce levels that are a feature of racing on this circuit. What we weren't expecting was the need to curtail Daniel's afternoon session.
"We stopped him early after seeing some markers in the data, related to his gearbox, that we thought prudent to explore. This leaves us with work to do to ensure we are competitive in qualifying and the race.
"It seems very tight this weekend with Ferrari and AlphaTauri in good shape, but we know what we have to do to meet our objectives over the next two days."
Video: The secrets of the Autodromo Hermanos Rodriguez circuit
Follow Rudy van Buren as he takes you on a flying lap around the Autodromo Hermanos Rodriguez, home of the F1 Mexican Grand Prix.