In the closing laps at Marina Bay, Verstappen was given a team order from the pit wall to allow Sainz to get past so that the Spaniard could have a shot at overtaking the Force India of Sergio Perez ahead which had been keeping both Toro Rossos bottled up.
Verstappen refused point blank, and while Sainz said afterwards that there were no bad feelings he nonetheless made headlines by saying that Verstappen "likes to play the bad boy role."
But asked by F1i about the prospect of damaging tensions escalating between the pair at the team's headquarters in Faenza, Italy, Tost brushed aside any such concerns.
"There is absolutely no issue between the drivers after what happened in Singapore," Tost said.
"They have a good relationship, a professional relationship as you could see in Suzuka at the end when Max - on the soft tyres - got the chance to overtake Carlos who was on the hard tyres and they finished in ninth and tenth."
There has been speculation that Sainz might be losing out in the psychological war against his younger team mate, who just turned 18 and immediately passed his road driving test on the same day.
But Tost said that there was no reason why Sainz should now have to forcibly stake out his claim and stand his ground in the remaining five races of the 2015 season.
"I don't think it's a case of having to respond. It always depends how the car is and in which position they are and which tyres they are on.
"Both drivers so far have shown really, really good performance."