World number one Novak Djokovic feels the pain of his long season during Serbia's Davis Cup semifinal with Argentina. Andy Murray and Andy Roddick are amongst those who believe top players are becoming injured more frequently because of the amount of matches they play.
Andy Roddick has been a strong advocate of a reduction in the ATP Tour calendar. The American former world number one believes the heavy schedule is resulting in players missing out on tournaments, which is not in their best interest. Getty Images
Tennis is not the only sport in which strike threats have been mooted. Just recently, Carlos Tevez (fourth right) reportedly refused to play for Manchester City against Bayern Munich, an allegation he later denied. Is it possible that top tennis players will do the same? Getty Images
The 2011 NBA lockout is the fourth in the competition's history. All pre-season matches and the first two weeks of the season have already been canceled. Getty Images
Espanyol football club tell fans that tickets are not for sale during the Spanish players' strike earlier this year. The 2011-12 La Liga season was delayed after players went on strike over unpaid wages. AFP/Getty Images
A dispute between NFL owners and players lasted over 18 weeks this year, although only one match was canceled.