Alonso was third in the world championship as recently as last month's Italian GP, but after a run of frustrating weekends, he now lies fifth, with Charles Leclerc, Lando Norris and George Russell all reeling him in.
Aston Martin meanwhile has fallen to fifth place in the constructors' championship but is under no threat from behind after being bettered by McLaren.
Alonso had another disappointing weekend in Mexico, starting 13th and then falling back after suffering suspected floor damage from debris left by Sergio Perez's first corner accident. The team eventually decided to retire the car.
His team-mate Lance Stroll started from the pitlane following a spec change, and was let through by the struggling Alonso before retiring after a late collision with Valtteri Bottas.
The Spaniard accepts that his slide down the championship table will continue.
"Honestly, we are not fighting for anything," he said when asked by Motorsport.com about the next race in Brazil.
"We will learn, even if we have to start from the pitlane, and you know that is more useful than just spending the weekend.
"In the constructors' championship, we are locked in in the position we are. In the driver's championship, we will lose a couple of places.
"But I mean, it is incredible that we are in front of Ferraris, or George or Lando or whatever, but we will lose those positions. They have a very fast car. And yet, let's see what we can do."
Alonso is adamant that the team is trying hard to get back on track.
"We are working as much as we can," he said. "It's not that we are just happy with the situation. It's not the position we wish we were, but at the same time, we are working very hard to reverse the situation.
"And sometimes you learn more from the difficulties than from the celebrations. So right now we have a difficult time.
"And we are trying to do as many tests as possible, giving as much feedback as possible to the factory in Silverstone. And hopefully, as I said, finish on a high, and not on a low."
Asked if things can improve within this season, he said: "I think so, we still need to go to three different places, three different circuits, which will give us more data again on the car.
"It depends on what we call finish on a high. If we think that we will fight for podiums or something like that? I don't think so. But to finish in a competitive way, I think we still have the possibility."
