usage note:

Of the two combinations self-depreciatory and self-deprecatory the former is, strictly speaking, the better-formed, since it reflects the long-established use of the verb depreciate in the sense ‘disparage, belittle’. The latter combination, however, which reflects the relatively recent use of deprecate in this sense, appears from the evidence to be now somewhat the commoner of the two. [OED online]

self-deprecating - 2.24 million gh
self-depreciating - 856,000 gh