SUGAWARA no Michizane praised Suenaga as he said in the "Kanke Bunso" (an anthology of Chinese-style poetry written by SUGAWARA no Michizane) that Suenaga was an irreplaceable person not only for the Imperial Court but also for this country, and Emperor Uda was severely shocked because he lost such an important person in addition to MINAMOTO no Yoshiari, who had passed away in the previous month.
菅原道真から「宮中要須之人也、聖主所照不更具陳」（『菅家文章』）と評価された季長の死は、前月の源能有の死に続くもので、宇多天皇（上皇）に大きな打撃を与えた。