Lots of threads...
But, Sir Cliff had a reasonable reaction.
Via his site and NME:
Cliff Richard 'very disappointed' about cancellation of his Morrissey support slot - NME
The post reads: "Cliff and the CRO are very disappointed to confirm that Morrissey has just cancelled the remaining dates on his tour, including the Barclay Center, Brooklyn, NYC on 21st June 2014 where Cliff was to perform as Morrissey's Special Guest."
It continues: "The CRO apologies for the inconvenience to fans and wishes Morrissey a full and speedy recovery."