Cotterill completed the signing of Stoke defender Ibrahima Sonko on a season-long loan earlier this week but Ritchie feels the squad is still lightweight.
Ritchie, who spent most of last season on loan at Notts County and then Swindon, said: "We haven't got the biggest squad but the lads that are here are sticking together.
"The older lads all helped me when I first came into the squad and now I can help some of the younger players.
"But hopefully we can strengthen the side a bit. We've brought in Sonko and that's a step in the right direction - hopefully we can bring a couple more in before the season starts."