Stephen Hawking, shown here at Cape Canaveral, Fla., in April 2007, was rushed to a hospital in April after fighting chest congestion for weeks. ((Peter Cosgrove/Associated Press))

Physicist Stephen Hawking's summer visit to Canada is on hold while he recovers from his recent illness, according to the head of the Waterloo, Ont.-based Perimeter Institute for Theoretical Physics.

Hawking was scheduled to visit the Perimeter Institute in the summer and give at least one public lecture, but in April he was rushed to Addenbrooke's Hospital in Cambridge, England after fighting a chest infection for weeks.

Institute director Neil Turok said the timing of the distinguished physicist's visit will be re-evaluated as he recovers.

"Stephen is hugely supportive of Perimeter Institute, and he is as disappointed as we are that his visit has to be postponed. But for now, we must be patient and wish him a speedy recuperation," Turok said in a statement Thursday evening.

Hawking, 67, suffers from a disease that damages the motor neurons in his brain and spinal cord, and belongs to the same family of diseases as amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease. He uses a wheelchair and speaks with the aid of a voice synthesizer.

He developed symptoms of the disease in the 1960s but has survived for decades and has, during that time, been one of the leading contributors to astrophysics, particularly with his work on black holes and his investigations into the origins of the universe.

Hawking, a professor at Cambridge, is perhaps best known for his book A Brief History of Time, one of the few physics books to become an international bestseller.

He is the Lucasian Professor of Mathematics at the Department of Applied Mathematics and Theoretical Physics at Cambridge University, a prestigious title once held by Isaac Newton.