Earlier this week, it was claimed that the Source Code star is romantically involved with Lowndes. A witness in New York City had told Us Weekly that the pair shared breakfast and then went to a party together on the same day.
However, the representative told Gossip Cop that rumours of a romance are untrue.
Gyllenhaal has previously been in relationships with actresses Kirsten Dunst and Reese Witherspoon, while he was believed to be dating Taylor Swift late last year. Recently, he has been linked with Rilo Kiley singer and former girlfriend Jenny Lewis and O.C. star Rachel Bilson.
Last month, the actor, also known for his roles in Donnie Darko and Brokeback Mountain, said that "everybody has the time to fall in love".
Watch the first five minutes of Source Code below: