Cyril Abiteboul says Red Bull blocked Renault's efforts to re-sign Carlos Sainz.
Sainz was merely 'on loan' from Red Bull this year, but the Spaniard will instead move to McLaren for 2019.
"It was strange," Russia's Championat quotes Renault boss Abiteboul as saying.
"In the end it was easier for us to sign Daniel (Ricciardo) than Carlos.
"Red Bull blocked our attempt to sign an agreement with Carlos. Around Paul Ricard we made a serious attempt to sign a full contract and Red Bull did not agree, as they were entitled.
"But in the end they still lost him as a driver, so it was strange to see," Abiteboul added.
The Frenchman says he is at least happy that Sainz is staying in F1.
"I have a slight feeling of regret, but we are glad he is at McLaren where there is a lot to do. And I don't have the feeling that any bridges are burned between him and us," said Abiteboul.