The body of Ms Leonard, 51, was discovered in Maguiresbridge last week.
Monday's attack is believed to have been carried out by Ms Leonard's former partner Peadar Phair, whose body was also found at her County Fermanagh house.
Ms Leonard's son Conor, who has Down's Syndrome, was also injured.
He had been stabbed in the stomach, and was taken to hospital where he received stitches for his wounds.
Conor, who is in his 30s, is thought to have summoned help via an alert system installed in their home.
Mr Leonard told BBC Radio Ulster's Sunday News programme that Conor is a very special person.
"Conor may have gifts that we don't even know he has," he said.
"He has a great network of friends and family.
"He has lots of great friends through his own network and I am sure there will be lots of professional people available to help Conor as well."
Mr Leonard added that the community in Maguiresbridge was very close-knit, and that his family appreciated the messages they had received.
"There's been support from right across the country, I've even had support from people that I've never met and probably will never meet," he said.
"It's all been a great source of strength to our family knowing that there are lots of people that care about us."
Mr Leonard said his nephew was taking it a step at a time to deal with the loss of his mother.
He described Conor as an "inspiration to all our family and friends" and that he was incredibly proud of him.
Ms Leonard had applied for a non-molestation order on Phair.
She was murdered a day before a court hearing had been due to take place in Enniskillen, in relation to the order.
Police are treating the attack on Conor Leonard as attempted murder. They are not looking for anyone else in connection with the stabbing.
Ms Leonard was well-known from her involvement with the Irish music organisation Comhaltas.
She also ran a catering business in Lisnaskea, County Fermanagh.
Concepta Leonard's brother Fergal has said the support his family has received since her murder is helping them to cope with their loss.