In all competitions the Saddlers have conceded in their last consecutive 17 games – including 15 league matches – last coming away with a clean sheet on November 3.
Alfie Bates’ mistake last week allowed Mansfield to equalise – one of many individual mistakes this season – and Clarke believes those errors have played a big role in the lack of clean sheets.
“It’s not good enough and it’s a major concern,” Clarke said.
“A lot of the games where we have conceded a goal is from a ridiculous individual error, that should have been a clean sheet. We’ve conceded only one goal in the league from a corner. We’ve been very good at defending set-pieces.
“There’s a lot of aspects in our defending that has been good but the lack of clean sheets is down to ridiculous individual errors. Our performances have probably warranted about eight or nine clean sheets to be honest. As any manager of coach will tell you, individual mistakes are very hard to rectify.”