Southend's automatic promotion hopes suffered another blow with a dismal 0-0 draw with Cambridge at Roots Hall.Neither side looked like scoring during an uneventful encounter which left the Shrimpers five points below third placed Wycombe who also have a game in hand on Phil Brown's side.Southend rarely threatened but just before half-time, winger David Worrall volleyed John White's right wing cross straight at Cambridge goalkeeper Chris Dunn.After the break, Cambridge striker Matt Harrold - who was facing his former side - headed straight at Daniel Bentley from 10 yards.But, with 73 minutes on the clock, the fifth-placed Shrimpers were forced to make their third substitution in worrying circumstances when centre-back Luke Prosser appeared to be knocked out by a well-struck Ryan Donaldson free-kick.Prosser received a lengthy spell of treatment from the medics before being stretchered off, wearing a neck brace.However, there was very little to excite the supporters in the closing stages of a very poor-quality game.