Paolini, who last year became the first Italian woman in the Open era to reach the Wimbledon final, lost 4-6, 6-4, 6-4 to Russian Kamilla Rakhimova last week.
The 29-year-old began working with Lopez in April after ending a decade-long partnership with Renzo Furlan.
Under the guidance of Lopez, a former doubles world number three who was once part of Rafael Nadal's coaching team, Paolini won her second WTA 1000-level crown at the Italian Open and also lifted the women's doubles title at the French Open.
"We had some great results together. Especially in Rome and Paris," Paolini wrote on social media on Monday. "I appreciate all the hard work and energy Marc gave every day.
"Now that this part of the season is over, I've decided to make a change. I've learned a lot and made good progress. And now I'm taking the time to reflect on what the next step will be. Thank you again, Marc, for everything."
