His head is in the clouds
(Slang) by analogy: He is not focused on the matter at hand. He is not adept in what is being done. A "dreamer".
(Modern Hebrew)
Translation
Expression (Hebrew)
הָרֹאשׁ שֶׁלּוֹ בָּעֲנָנִים
Definition (Hebrew)
(סְלָאנֶג) בְּהַשְׁאָלָה: אֵינוֹ מְרֻכָּז בְּעִנְיְנֵי הִמְצֵאת. אֵינוֹ בָּקִי בַּנַּעֲשֶׂה. "רַחֲפָן".
(הָעִבְרִית הַחֲדָשָׁה)