The pair are fighting it out for the Formula One title this season, with Rosberg leading the race by four points.
In scenes reminiscent to the long-running feud between Red Bull pair Sebastian Vettel and Mark Webber, the battle to be crowned world champion appears to have affected Hamilton and Rosberg’s relationship.
And Kubica feels that Mercedes’ complete dominance of the 2014 campaign – they have won all six races contested this year – will only make matters worse.
“When you are only fighting against your team-mate, it can get quite difficult,” Kubica told Autosport.
“If there are some other drivers close, you have to focus to finish second, but in the current situation Nico and Lewis need to have a very bad day not to finish in the top two.
“Now they know they are only driving against each other as the others aren’t something to worry about because Mercedes has such a big advantage.
“It’s not easy, but they know each other very well and I think it is not as bad as the media would like to see it.
“But it would be tense because that is normal when you are fighting for wins and the championship.”
Kubica feels Mercedes bosses Toto Wolff and Niki Lauda have key roles to play in cooling the ongoing tension between the duo.
“In the current situation, Toto and Niki have a big role,” said Kubica.
“I remember I was watching the race in Bahrain and there was a shot of Toto on the pitwall, for sure I would not like to be in his position.
“It is a delicate situation because you have two great drivers with a big car advantage over the others.”
The 2014 Formula One season next stops in Canada, with the main race to be held on Sunday.