International Debut For Toon Star 'Put On Hold'!
Hungary ran out 3-2 winners over the Greeks.
The youngster is back on Tyneside and underwent a scan on his knee before discovering the injury will require a minor operation.
Kadar will undergo surgery on Saturday, which puts a question mark over his involvement in the Under-19 European Championship finals in the Czech Republic, which start on July 14.
The 18-year-old has yet to make his first-team appearance for United.