Barack Obama has paid tribute to Hillary Clinton, for being a woman who 'keeps on going'.

The U.S. presidential candidate revealed she is suffering with pneumonia after being seen lurching into the arms of her security officers at the weekend.

The Democrat has since revealed she ignored her doctor's advice to take a break, sparking criticism.

But, speaking at a rally in Philadelphia, the current president says she doesn't deserve that:

 Hillary Clinton's husband, the former president Bill Clinton, has revealed the collapse at the weekend wasn't the first such incident.

Bill Clinton's been talking to Charlie Rose on CBS Digital and says Hillary has previously suffered from severe dehydration: