得 in complement of degree or manner

Hi everybody. This question belongs to the "I know how to use it, but grammarwise it does not make sense to me". Here goes: "Please speak a little slower" is rendered "qǐng shuō màn yīdiǎn" by native speakers, why is no 得 inserted between shuō and màn?

is it because the implied object 話 omitted?

cheers

阿賓