The Olympic and World Champion Femke Bol was one of the many people to publish messages of support for Mageeean.
The Dutch corridor said he was sending him “love and strength.”
Mageean’s Irish teammate, Sarah Lavin, said: “I don’t have the words to send you. You are so loved and so strong and wish I could give you the greatest hug.”
The double Olympic boxing champion of Ireland, Kellie Harrington, said “we all love you and pray for you and keep positive spirits for you.”
European Athletics published in X: “We are all behind you, Ciara. All in European Athletics send their best wishes to Ciara Mageean after their recently diagnosis of cancer.”
Portaperry Gaa, whom Magean used to represent in Camogie, said it is “really an inspiration for so many people.”
“We are all behind you in this fight,” said the club.
“You and your family, as always, have our full support in each step of the road.
“We know that you will make it better and strong. We send you our love and the best wishes.”