Gyllenhaal, 32, is said to have met the 22-year-old model in a spin class at a SoulCycle in Manhattan last fall. The actor and DiDonato have dated for past two months, reported Us magazine.
"He'll hop on the instructor bike. He loves the attention from the girls!," a source said.
Gyllenhaal had a brief romance with Minka Kelly last summer. But his last serious relationship was with country singer Taylor Swift.