There are different motivations for different people. The top motivations for high performers I can think of are:
a. For some, challenging tasks will be a high motivation or giving more responsibility is a high motivation.
b. For some, constant appreciation/reward is motivation.
c. For some, travel is motivation. For some, appraisal/promotion is motivation.
d. For some, team leading or role change is motivation.
e. For some, getting training to keep his/her knowledge up-to-date is motivation.
I will identify what does motivate him/her based on the above criteria and will try to align that activity to him/her after having a word with my seniors, if it is doable.
If not, see when it can be done in the future and let him/her know.