Daniel Ricciardo says he was unaware that Max Verstappen had been given an upgraded engine for this weekend's United States Grand Prix.
Ricciardo also claimed he did not realised that the Dutchman will hold a performance advantage until the end of the campaign.
For the Austin weekend, Renault has given one version of its updated power unit, which includes 2018 development parts, to each of its three teams.
It is then up to those teams to decide which driver runs it.
At Renault, Nico Hulkenberg has got the new specification and Brendon Hartley is running it at Toro Rosso, while Verstappen has been given the Red Bull version.
They are the only three updated engines that will be made available this season, which means that if the other Renault drivers need to change a power unit then they will have to stick to the older spec.
There have been suggestions the new unit is worth up to two tenths of a second.
Asked about how big a disadvantage he felt he had with running the old engine, Ricciardo said: "We had different engine specs? I had no idea.
"Seriously - I didn't know. Whose was faster?"
When told that Verstappen, who qualified behind him in sixth place before dropping 15 further places thanks to grid penalty he received for taking the new engine, held the advantage, Ricciardo smiled as he punched the air in delight.
It is likely that Ricciardo will change engines at the next race in Mexico, even though there is a chance he could get through the campaign with his current power unit.
"I believe I will have to take another penalty and I believe I will have a grid penalty in the next three races," he said.
"I would like to say no I won't, but it is probably more likely than not at this stage."
When pushed on if he felt any disappointment about having a different specification of engine to Verstappen, Ricciardo joked: "Oh, so that is why Max signed his contract! I literally had no idea.
"Maybe they told me and I chose not to listen - but if that is the case I'll just charge my way through."
Jumping Bottas key to fighting Mercedes and Ferrari
Although Red Bull was unable to match Mercedes and Ferrari in qualifying at Austin, Ricciardo, who will start fourth, thinks that he can take the fight to the front in the race - if he jumps Valtteri Bottas for third place at the start.
"I have to put myself there at the start," he said.
"I really need to try to jump Valtteri and put myself with Lewis [Hamilton] and Seb [Vettel] to try to run with them, and then we will go from there.
"That last run [in Q3] was encouraging. Q1 I was like over a second off the pace and we were a long way from where we needed to be, so we found a lot of time in that one hour."