The Italian was struggling physically during his loss to Rublev in Montreal on Saturday night.
The 20-year-old says she took a lot from mingling with American stars such as gold medal winners Sydney McLaughlin-Levrone and Gabby Thomas.
The Greek shared the news on social media on Friday.
The Greek sent a message to his father and coach through the media.
The 24-time major champion will take some rest before the US Open.
"It hurts. It hurts. It hurts," said Grigor Dimitrov after surviving every male player's nightmare in Montreal.
Mexico's Renata Zarazua moves into the US Open main draw.
