Without oxygen and low on energy, Mike yields to Rob (9)
I believe the answer is:
anaerobic
'without oxygen' is the definition.
'and low on energy mike yields to rob' is the wordplay.
I cannot quite see how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is found in the answer.
'energy' could be 'e' (physics symbol as in E=mc2) and 'e' is present in the answer.
'to rob' could be 'rob' and 'rob' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for anaerobic that I've seen before include "lacking in inspiration?" , "functional without O2" .)