Need advice

My friend gave a blank cheque at a grocery store for the purchases he had made. The store owner is known to him and normally he pays by cheque and this time he had paid blank cheque as he had leave on an emergency. The store owner now says he has used this cheque to get a loan for himself but by submitting this cheque to a financier. He is asking my friend to repay as otherwise the financier will submit the cheque to bank. What are my friend's options to defend. Looks like my friend has nether met the financier nor signed any document except that his blank check is with the financier. Thank you in advance.