When Svetlana Kuznetsova had to leave her dog, Dolce, at home in Russia this spring when she left for a tournament in California, she cried.

She cried in the airport. She cried on the plane. And she cried again in her hotel room, a place that can be lonely for Kuznetsova, a former United States Open champion who spends as many as eight months of every year on the road.

“I cried and cried, for three days I cried,” she told me last week.

Kuznetsova, a two-time Grand Slam champion, went on to detail for me a dark side of professional tennis virtually invisible to the average fan. It’s the part tinged with isolation and sometimes depression, brought on by months on the road away from friends and family. It’s weeks and months and years on end sacrificing real life for a tennis life, without a real home: constantly parachuting into different cities and setting up camp in strange hotels.

This is the bargain pros make, the sacrifice that is paid back with prestige and prize money — more than $23 million to date for Kuznetsova. But she is still a human being, susceptible to personal disappointments and professional failings, and when one views her life through that lens, it’s clearer to see how a dog like Dolce can be as vital to her as the right racket or a good hitting partner.