John Harbaugh has said that the Baltimore Ravens defense must work on their communication.

The Super Bowl champions could have up to seven new faces in their starting lineup for the 2013 NFL season.

The head coach told the Ravens' website: "Communication is the final piece. We've got a lot of communication issues on defense that came up, things we need to work on.

"From a cohesion standpoint, we have a lot of work to do. Penalties and mistakes. If we don't do that on defense, people are going to have a tough time moving the ball on us."

The Ravens beat the Tampa Bay Buccaneers in their opening pre-season game on Thursday.