Carlos Sainz has questioned his boss's target of a podium finish on merit in 2016.
The Red Bull junior team's chief Franz Tost declared recently: "Realistically, I expect that we can achieve a podium this year after getting so close to it last year."
Toro Rosso has switched from Renault to the more powerful, 2015-specification Ferrari engine, although it will not be developed throughout the season.
As for Tost's podium prediction, however, Sainz is quoted as saying by El Mundo Deportivo: "I think the chance of a podium is low. Under normal circumstances, I don't think it's possible.
"Mercedes and Ferrari are on another planet, and Williams and Red Bull should be behind them. We aspire to be the fifth team on the grid, so from ninth or 10th it is not easy to reach the podium.
"To do that, the circumstances would need to be abnormal."
Toro Rosso finished seventh in last year's standings.
