The double world champion dropped out of the points in Austin when stewards upheld a post-race Haas protest against him being allowed to continue with a loose mirror that eventually fell off.
Renault-owned Alpine then protested the admissibility of the Haas protest.
A video hearing was scheduled at the Mexican Grand Prix later on Thursday with the U.S. stewards on whether to consider Alpine's protest.
"I am very optimistic that we will keep seventh place," Alonso told reporters at the Autodromo Hermanos Rodriguez.
"The FIA has been very transparent to us this year... so I fully trust what they will decide.
"I think there are a couple of things that are very clear that were made wrong from their side. I am very confident that I will P7 again."
Alonso said stewards had made the wrong decision and sticking with it would "open a huge problem for the future in Formula One.
"I think 50, 60, 70% of the cars will have to retire when they have an aerodynamic device that is not properly fixed," he said.
"If 20 minutes too late is OK to protest, is one month too late? Is one hour too late? Is 10 years too late? When is too late? That I think we cannot afford (that)," he added.
Haas had argued that Alonso's car was in an unsafe condition after a collision because the right-hand mirror was moving around.
They also made the point they had been shown a black and orange flag, requiring a driver to pit due to mechanical problems or loose bodywork, on three occasions this season whereas Alonso was not.
Alpine said Haas had lodged their protest 24 minutes too late and it should not have been accepted.
Alpine would have scored six points for Alonso's seventh place but instead ended up with just one for Esteban Ocon (26) being bumped up to 10th. That left Alpine only six clear of McLaren with three races remaining.
Alonso's demotion lifted Haas's Kevin Magnussen (30) from ninth to eighth, doubling his points haul from the race.
