The Championship side said that the 26-year-old's "physical and mental wellbeing are our number one priority at this moment in time".

"Angus has shown great strength of character in the way he has reacted to this news," they said in a statement.

"The whole Tigers family join together in showing Angus continued love and will support him in his recovery."

MacDonald missed almost all of last season after being diagnosed with deep vein thrombosis in November 2018.

The centre-half, who started his career with Reading and joined Hull from Barnsley in January 2018, previously suffered from a blood clot on the lung at the age of 15, but made a full recovery.