Yacob joined the Baggies on a free transfer from Racing Club in Buenos Aires and has become an instant hit.
"When you spend the amount of money we did on Yacob and he turns out to be as good a player as he is for the team, that's great," said Clarke.
"Normally a player of Claudio's type is a players' player, a manager's player or a coaches' player and doesn't really stand out - he just does his job for the team.
"But in doing the job for our team he has managed to stand out as being exceptionally good at it. I think he's been tremendous and a big, big bonus for us.
"I hadn't seen him but, either on my first or second day, here I got given a pile of DVDs. I went through them all and thought 'I quite like that one'."