The 30-year-old said in a statement: "I have recently been diagnosed with cancer of the liver.
"I'm currently undergoing treatment and fighting this illness with everything I have."
Baltacha was diagnosed at the age of 19 with primary sclerosing cholangitis, a chronic liver condition which compromises the immune system.
Ukraine-born, she won 11 singles titles, reached the third round of Wimbledon in 2002 and the same stage of the Australian Open in 2005 and 2010.
Son of former Ipswich, St Mirren and Inverness footballer Sergei, she reached a career-high ranking of 49 in 2010 and was British number one for 132 weeks between 2009 and 2012.
However, she struggled with injury and illness during her career and retired from the sport in November last year.
The statement continued: "Elena and her husband Nino would like to thank everyone for their continued support."
Baltacha also played Fed Cup tennis for Great Britain for 11 years.
Current team captain Judy Murray told www.lta.org.uk: "Obviously this is a tough time for Bally, Nino and her family but she is a such a determined, upbeat person and everyone around her is staying positive as well.
"I know she'll be really grateful for all the support that she's getting."
Following her retirement, Baltacha had vowed to concentrate on developing junior players at her Ipswich-based academy.
She can look to Great Britain Davis Cup player Ross Hutchins for inspiration.
The 29-year-old, this week appointed the new tournament director of London's Aegon Championships, returned to action earlier this year with doubles partner Colin Fleming after recovering from Hodgkins Lymphoma - a form of cancer.
Hutchins was diagnosed with the illness in December 2012 but announced he was in remission in July.
For several years Baltacha and Anne Keothavong headed up the women's game in Britain.
The latter has also retired and she issued a message of support to her old rival on Friday afternoon via Twitter.
It read: "She's one of the people I most admire for her courage and determination. You'll fight through this @ElenaBaltacha xxx."