Cotterill brings his men to the City Ground on Saturday to face Nottingham Forest on the back of an FA Cup defeat at Brighton, continuing financial woes and a rapidly shrinking squad.
'I think a little bit of what has been going on off the pitch has been affecting the players, probably over the past couple of weeks,' he told local newspaper The News.
Cotterill has been unable to call on Michael Brown and Richard Hughes due to contractual issues and has a number of injury and suspension problems to deal with.
He added however: 'We've got some great fans who give their all to the club and we certainly can't give in.
'We just need a few more to go with those players.
'When they are tired and on their heels a little bit, you just want to call on a couple more.'