Aretha Franklin has cancelled two concerts due to undisclosed medical reasons.

The soul legend has pulled out of a show with the Chicago Symphony Orchestra on May 20, and a solo performance at Connecticut's Foxwoods Resort Casino on May 26, but the specific reason why has not yet been disclosed.

Foxwoods spokesperson Dale Wolbrink said only: ''It was cancelled for medical reasons.''

The Chicago Symphony Orchestra said Aretha, 71, cancelled her performance due to a ''doctor's recommendation for treatment during the time frame of May 20 and 26.''

Singer Janelle Monae will now fill in at the Chicago show.

Aretha is still scheduled to perform three shows next month, with two concerts planned in Canada and one in Michigan.

The 'Respect' singer pulled out of concerts in 2010 and underwent surgery for an undisclosed complaint, prompting speculation at the time she was suffering from cancer.

However, she dismissed the claims a month later, insisting her problems were ''resolved'', though her recovery was slow.

She added at the time: ''I feel great. The doctors say I can do whatever I feel like I am up to do. Of course, that doesn't mean any concerts or anything like that.

''But I can do things around the house, and today I am just piddling around the house. It is good to sit up, too. I also might make one or two business calls. Not too much, just a teeny bit.''