"Nico and Lewis are very close to each other," Haug, now a commentator for the German touring car series DTM, claimed in an interview with Bild newspaper.
"Each of them has a good chance of dominating the rest of the season," he added.
The battle between Rosberg and Hamilton is likely to be a focal point of the rest of the 2014 season, given Mercedes' current dominance over the other top teams.
"I hope it will be a close duel between them for a long time," said Haug.
He denied he has a favourite: Rosberg, who he worked with at Brackley since 2010, or Hamilton, whose career dates all the way back to his junior years with the Mercedes young driver programme.
"No, I like them both," said Haug. "I have known Lewis and Nico since they were kids and I'm proud of them both.
"I hope we see many more hard, exciting races as we did recently in Bahrain. But it's also clear that there is a loser and a winner at the end of every duel.
"Hero and zero is never far away in motor sport," he smiled.