Stoke, who are without a manager after Mark Hughes was sacked following Saturday's 2-1 defeat, have endured a poor run of form and are in the Premier League relegation zone after just five wins this season.
"We can't get much lower at the minute, it's been a tough time of late and everyone can see that," the England international told the Stoke Sentinel. "We're not happy with the way we're playing. Everyone is pretty low and it does feel like the only way we can go from here is upwards.
"There's only us that can change it and we have to make sure we do. Like the result at Coventry it's embarrassing and difficult to swallow. It's only ourselves to blame as a team, we've given up too many chances, we've not defended well as a team, too many individual errors.
"Whether it's a lack of confidence or not defending well enough as a team or being too exposed, we've not been good enough. It's something we need to address and get a hell of a lot better. We're giving ourselves a mountain to climb if we've got to score two or three goals every game to get a result."
Stoke are expected to consider potential replacements for Hughes this week, ahead of the Potters' tie with Manchester United next Monday.