Red Bull and Toro Rosso have admitted that there is a chance that they may choose not to race Renault's upgraded Formula 1 engine when it finally becomes available.
Renault has not yet used any of its 12 tokens, and the long-awaited upgraded D-spec is now not expected to be available before the United States GP, leaving just four races in which it could be deployed, with the first inevitably compromised by a grid penalty.
At Monza, both teams made sufficient engine changes to get all four cars through to the end of the season with the current power unit and without further changes, and thus grid penalties.
If any of the drivers takes the upgrade, they would have to take an extra penalty in Austin in order to have use of a potentially stronger straightline package, and no more penalties, for the last three races.
Red Bull's situation changed when one of Daniel Ricciardo's new engines suffered a failure in FP3 in Italy, so the Australian is now obliged to make an extra change anyway, and take a penalty.
Logic suggests that the team will attempt to postpone that change until Austin and thus give Ricciardo the upgrade for the end of the season races.
However, the decision on whether to stick with the proven old spec or go to the new one will involve weighing the potential increase in performance against any reliability risks associated with the upgrade.
Christian Horner admitted that it could transpire that neither Red Bull driver will actually use the revised engine.
"It's a possibility," he told Motorsport.com. "It depends on the value of the update. What you have to calculate is is the increase performance worth the deficit of grid positions?
"I think with Ricciardo he is going to have to take another engine, so theoretically that should be the D-spec if it's reliable.
"At the moment I think a lot of work is being done in the background to make it reliable. It's not a great situation obviously, but it is what it is, and we've just got to try and battle on through it.
"It's beyond frustration, we've just got to deal with what we've got on a race-by-race basis."
Gains could make it worth it
Meanwhile, Toro Rosso boss Franz Tost agreed that the potential performance increased was the key, and admitted that it could be worth taking the penalty in Austin if that led to a boost over the remaining three races.
"There are always different reasons behind an engine change," he told Motorsport.com. "First of all we need a performance advantage behind it, otherwise it doesn't make sense. Up to now we don't have all the information about the D-spec. We will see.
"Of course if the D-spec is much better than the current one, we will take another penalty, because we need to show the best possible performance, and we need to take this advantage.
"After Austin in Mexico there's a long straight, and in Sao Paulo there's a very long straight. We need the best possible engine.
"If you ask me now from my personal opinion, then yes. But this is also a decision from the engineering side, not only my side."