Daniel, who has a preference for non-celebrity girlfriends, started dating production assistant Rosie more than a year ago, but the pair haven't been seen together in months.
The actor was spotted outside a club in Chelsea with a mystery brunette last week.
An onlooker told the Daily Star, "She initially did everything she could not to be seen with Daniel but she probably realised there wasn't much point in trying to hide. She then went to the other extreme and linked arms making it look like they're a couple.
"Daniel looked really relaxed and happy with her. It was obvious they'd had a nice evening together.
"Anyone who didn't know he had a girlfriend might have thought it was a date."
Dan was spotted out with a different girl last month, sparking rumours that his relationship had ended.
"For someone with a girlfriend Daniel does spend a lot of time with other girls," an insider told the Daily Star. "They could be just friends but it's been two in less than a month so fans are going to start thinking he's definitely split from Rosie."