Laid up with a nasty face! (4)
I believe the answer is:
dial
'nasty face' is the definition.
'dial' can be an answer for 'face' (face of a clock). I'm unsure of the 'nasty' bit.
'laid up' is the wordplay.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'laid' in reverse letter order is 'DIAL'.
'with a' acts as a link.
Can you help me to learn more?
(Other definitions for dial that I've seen before include "Calibrated face" , "Ring the clock-face" , "Indicator" , "Calibrated disc etc" , "Laid up like clock-face" .)