THEY'RE back.

Andy Murray, Novak Djokovic and Rafael Nadal all play in their first tournament since Wimbledon this week when they contest the Rogers Cup in Montreal. Significantly, Roger Federer has withdrawn.

Three of the Big Four thus return to a tennis circuit that has not failed to provide storylines since Murray won in SW19.

These dramas can be crudely summarised as drugs and decline.

Viktor Troicki, of Serbia, was given an 18-month ban for failing to provide a blood sample in Monte Carlo. It has also been disclosed that Marin Cilic, of Croatia, failed a drug test in Munich. Cilic was not notified of the positive test until before his second-round match at Wimbledon, then pulled out, citing a knee injury. Cilic's manager has claimed the player failed a test because of "incautious use of glucose". The International Tennis Federation have not commented, perhaps because an investigation is ongoing.

These cases will cause further comment by the top players, particularly Murray and Federer. Both were outspoken at the ATP World Tour Masters finals in November. The Scot and Swiss both want better, more stringent and more regular testing. Their campaign will be bolstered by events of recent months.

On court, Federer faces a different challenge. He is the subject of undoubted decline with his post-Wimbledon form alarming.

The 17-time Grand Slam winner will be 32 this week and lost to the world No 55, Daniel Brands, in straight sets in the first round of the Swiss Open. This was his first opening-round loss since 2010 and the third consecutive tournament in which he has lost to a player ranked outside the top 50. He also lost in the semi-final of the German Championships in his first tournament since losing to Sergiy Stakhovsky at Wimbledon.

He has won one ATP 250 tournament and reached the semi-final of one Grand Slam this year and this constitutes his worst campaign in more than a decade. The last time he recorded three losses in a row against players ranked outside the top 50 was in 1999, when he was 18 and ranked below No 100.

He is trying to play with a bigger racket, is undoubtedly hampered by his long-standing back injury and has much to ponder before the US Open this month.

Federer has solid claims to being the best player of all time but there are more than hints of sporting mortality. He is capable of winning big tournaments but there are going to be more defeats on his cv while the intensity of the work remains and the ability of the body to accept this diminishes.

His absence in Montreal robs the tournament of an intriguing element and the catalyst for a running debate on whether the great man is in severe decline leading to imminent retirement or whether he still has enough fitness and reaction speed to be a contender at the very top.

Between them, Djokovic, Murray and Nadal have won the Canada title seven times. Djokovic is the two-time defending champion and is bidding to win the title for the fourth time, having also triumphed in 2007. Murray won in 2009 and 2010, while Nadal lifted the trophy in 2005 and 2008.

The Spaniard will be scrutinised for any signs that his knees are beginning to fail him. At Wimbledon, he found the repeated movements to crouch to engineer shots caused him debilitating pain. The clay of Roland Garros is kind on his body because he has to reach rather than bend for his shots but the hardcourts are punishing on all joints, particularly the knees.

The favourites, then, will be Djokovic and Murray. The straight-sets defeat inflicted on the world No 1 by the Scot at Wimbledon could be a significant moment in the history of a rivalry that stretches back to the juniors.

Murray has won two of the three most recent Grand Slam finals they have contested and knocked the Serb out of the Olympics. He has no fear of Djokovic and prepares for his defence of the US Open with a burgeoning confidence.

The sub-plots are of drugs and decline but Murray will be looking for the leading role as champion in Montreal and, more pertinently, Flushing Meadows.