If clearance hasn't come through, I presume his contract isn't yet valid. If he's still registered with another club, he might not be eligible to play in any games until the registration is officially cleared.
The AN Other type characters generally seem to be amateur players who are dipping their toe in the pro-ranks for the first time.
It'll be really disappointing if Mitch can't play a part on Sunday.
If he's signed a contract with us surely he can't still be registered with someone else. It's only a warm up game get him on the pitch. So he gets a warm up cos he will need it on sunday.