Pompey are currently under a transfer embargo leaving Cotterill with a threadbare squad to work with as they build up towards the npower Championship season.
Cotterill watched as a mixture of youth and experience got Pompey's pre-season programme off to a winning start with a 2-1 success against Havant & Waterlooville, with David Nugent and Michael Brown on target.
"The senior guys are top lads," said Cotterill. "It would be easy for them to buckle when they look round and see all the young lads playing with them.
"But that's the situation we've got. The embargo is there and there's not a lot we can do about that.
"We haven't got a lot of bodies - Marlon Pack went off but then he had to go back on a bit later. It's not ideal but we know the situation and we have to keep on working hard."