One foot in the grave
To be near to death.
The phrase 'one foot in the grave' has been current in English since the 17th century. It is rather an antiquated expression but took an upswing in use, in the UK at least, following the success of the BBC sitcom One Foot In The Grave, which was popular throughout the 1990s and starred Richard Wilson as grumpy old man Victor Meldrew.
It is fairly easy to derive the meaning of the phrase as 'close to death'.
The first example of the expression in print is found in Philip Massinger's and Nathan Field's play The Fatall Dowry: A Tragedy, 1632:
When one foot's in the graue.
17th century listeners would have had a different understanding of this than we do now. 'Foot' was then used as a verb meaning 'trip' or 'catch'. To 'catch by the foot' was to hold someone, as if in a trap. A figurative expression like 'one foot in the grave' would have then been understood to mean 'trapped by death' with no possibility of escape.
Other 'One' phrases: