Toto Wolff has admitted continuing to supply McLaren with Mercedes engines next year is "not a pleasant situation".
McLaren has already announced its intention to unite for a works collaboration with Honda in 2015, raising fears Mercedes' IP could leak into the Japanese carmaker's turbo V6 design.
"Supplying McLaren for one more year is indeed not a pleasant situation," Mercedes motor sport chief Wolff is quoted by Kleine Zeitung newspaper.
"But I'm confident that McLaren will abide by the rules of the contract and not share any data (with Honda)."
Wolff also played down reports the new V6 rules have dangerously ramped up the prices of formula one engines for the suppliers' customer teams.
"With the longer running life and low consumption, they will be cheaper over time," he insisted.
Indeed, the turbo V6 rules are already making sense for Toro Rosso, having switched from Ferrari to Renault power for 2014.
Renault's V6 engine is reportedly the most expensive of all, but the deal means Toro Rosso can now use the same gearbox as sister team Red Bull next year.
"This synergy with Red Bull is important," said team boss Franz Tost.