Yacob is out for a second successive match with a hamstring injury, while Mulumbu is suspended after picking up five yellow cards.
But Clarke insists he is happy with the alternative options he has in midfield, stating that he has players that can replace the absent duo.
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"We're in a much better situation than last week. We had a few players playing with little problems, which is good because it shows the character in the squad – they want to push themselves through the pain barrier.
"We've got other midfield players who can slot in there.
"Obviously you don't like some of your players to be out missing but I've got no worries about the boys that come in – they'll do the job.
"Chris Brunt went in there last week and did well, James Morrison has played in there this season and in previous seasons and done well.
"Graham Dorrans is a central midfield player, Zoltan Gera can play in there, I've also got Gonzalo Jara Reyes, who can play in there. It's not something that overly concerns me."
Clarke also suggests he may recall 21-year-old striker Chris Wood from his loan period at Millwall, even though the Baggies are not expected to re-negotiate the New Zealand international's contract at the end of the season.
"Chris is one of our players who is out on loan at the moment and doing fantastically well," he added.
"He's got a lot of clubs interested in him but at the moment he's still an Albion player and if I need him to come back here next month and help us, that's what we will do."