LONDON (Reuters) - The difficult relationship between Lewis Hamilton and Nico Rosberg has become a weakness for Formula One champions Mercedes and it could affect future driver decisions, team boss Toto Wolff warned on Wednesday.
"We struggle sometimes in winning races on Sunday and having always one (driver) upset," the Mercedes motorsport head told motorsport.com.
"And this spills over into the team. It is something that needs to stop."
Hamilton and Rosberg have been rivals since their early teens as team mates in karting but the once-warm relationship has been stretched to breaking point at dominant Mercedes.
The Briton and German were barely on speaking terms at times last season and entered another frosty phase this year after Hamilton clinched his second title in a row and third overall in Texas in October.
Rosberg ended the season in Abu Dhabi on Sunday with his third successive win and sixth pole position in a row, a run that soured Hamilton's mood and left him questioning the strategy.
"We took the decision of having two evenly matched drivers in order to make the team progress faster and better," said Wolff of the decision to pair Hamilton, who joined from McLaren in 2013, and Rosberg.
"Going forward, we will consider if it is the best set-up for the team. Personality and character within the team is a crucial ingredient for the team success.
"If we feel that it is not aligned with the general consensus, spirit and philosophy within the team, we might consider that when we take a decision, in terms of the driver line-up going forward."
Hamilton has three more years while Rosberg is signed to the end of 2016 with a team that this year won 16 of 19 races and enjoyed a record 12 one-two finishes.
While Hamilton has spoken of seeing out his career with Mercedes, Rosberg's position would be weakened anyway if he finished second again next year.
Wolff indicated the drivers' behavior off the track was also important.
"I think it is important to have talented and fast drivers in the car. But we want to work with nice guys," he said.
"We are having huge unity within the team, but the difficult relationship of the drivers is one of our weaknesses. And that is not good."
"The biggest weakness is the dynamic of the relationship between the drivers -- and sometimes between the drivers and the team."
(Reporting by Alan Baldwin, editing by Clare Fallon)