Yes he can. But he won't be able to play for the previous clan in CL 12, in case he wants to switch back to it after CL 11.
Edit: Actually i have to correct myself and quote the CL 10 rules.
If a player is present on Clan X’s roster in a given season, and decides to leave clan X to play for another Clan Y. This player cannot play for Clan X again for another 2 seasons. The only exception to this rule is if Clan X drops out of the Clan League.
Edited 9/21/2018 16:52:26
This rule accounts for all rosters from CL8 onwards, so if a player represented Clan X in CL8 and Clan Y in CL9, they cannot play for Clan X again until CL 12. Seasons before CL8 are not considered.