Depends whether cheques are crossed. If cheque is crossed "account Payee only" then you have a prob.
If cheque is crossed with no other writing or with the words "& Co" in the crossing, then a bank may accept it from your mate if it was endorsed by both of you. Endorsing is just signing on the back.
If it is not crossed (this is unlikely but possible), then it should be straightforward, provided you both endorse it.