Anti-apartheid struggle stalwart Ahmed Kathrada’s recovery from his operation has been “slower than hoped for”, his foundation said on Wednesday.

Kathrada was hospitalised on March 4 for surgery related to blood clotting on the brain.

The foundation’s director Neeshan Balton said in a statement that Kathrada had "experienced several health-related setbacks making the prognosis of his illness unpredictable".

"He remains in hospital with everything being done to assist his recovery," Balton said.

He said visits from members of the public were still not permitted due to hospital regulations and the necessity for a restful period of recovery.

"We have been overwhelmed by the immense support, both from within South Africa and abroad. We continue asking for your prayers during this period, both for Mr Kathrada and his family and friends," Balton said.

The 87-year-old had initially been admitted to hospital for dehydration, but doctors later picked up the clot, which was removed.

Kathrada is one of three Rivonia trialists still alive today - the other two being Andrew Mlangeni and Denis Goldberg.