Mason, 26, sustained a fractured skull in a clash of heads with Cahill while defending a corner during his team's defeat and subsequently received treatment for around nine minutes on the Stamford Bridge pitch.
"Devastated to hear today's news from Ryan", he tweeted.
"Of course the door is open to help him; everybody at the club loves him and all his family".
Mason had hoped to make a comeback this season but announced on Tuesday, because of further medical advice, that he had been forced to hang up his boots.
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The player can see the indicators for other squadmates on the map, and the battlefield will get continuous supply drops. However, some variants of the weapon would still be present in the game.
Mason also earned one England cap while still a Spurs player in 2015, playing Italy - coincidentally - in Turin.
And now Harry Kane has sent a heartfelt message on Twitter, saying, "So proud to have come through the system and played at the highest level with you". To have had the honour of captaining the team fills me with enormous pride.
"Finally, representing my country is an honour that nobody can ever take away from me and something that I am so proud to have achieved".
'Ryan has sought the guidance of numerous world renowned neurologists and neuro surgeons who have all advised that a return to competitive football is not advised.
Mason began his career at Tottenham and had loan spells with Yeovil, Doncaster, Millwall and Swindon before joining Hull in a £12m move in 2016.
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Mason stretchered off after the collision with Cahill.
'Don't worry Ryan because you are going to be a successful person in football outside of the pitch, no doubt about that'.
"In my three years, nine months he has always been important for us, stepping up and growing up".
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US Intelligence chiefs said Tuesday that North Korea will be one of the most confrontational threats to the US this year.