Controversial sprinter Justin Gatlin has been given a new sponsorship deal by US sportswear giant Nike.

The 33-year-old American dominated the 100m and 200m in 2014, and is some experts' favourite   to win a golden double at August's World Championships.

But Gatlin is a divisive figure, having served two doping bans, including a four-year suspension between 2006-2010.

Ex-Team GB star Jason Gardener said: "Nothing surprises me but this another bad message being sent by our sport."

The former world indoor and Olympic 4x100m champion added that there was mounting evidence that "systematic dopers" gained long-term residual benefits from their cheating, so repeat offenders needed much harsher punishments.

Marlon Devonish agreed with his teammate from that 2004 Olympic relay quartet, saying news of Gatlin's contract will be a "kick in the teeth to the 99% of guys who are clean" but that this was a matter for the rule-makers to deal with.

"No, it doesn't sit well with me," said Devonish, who won four world relay medals between 1999 and 2009.

"But Gatlin has served his ban according to the rules: if people don't like that, change the rules."

Gatlin was sponsored by Nike prior to his second ban but has been wearing Chinese firm Xtep's kit since 2012.

His US teammate Tyson Gay, who has also recently returned from adrugs ban, will also be wearing Nike clothes and spikes this season, although the company denies this is a result of a formal tie-in.

The Oregon-based company said Gay, who was dropped by Adidas when he tested for a banned substance in 2013, is getting its equipment because he has started working with the Nike-sponsored coach John Smith in Los Angeles.

The 32-year-old Gay claimed a hat-trick of sprint medals at the 2007 World Championships in Osaka, and is still the joint second-fastest man over 100m with a personal best of 9.69 seconds, but he has struggled to win individual honours during the Usain Bolt era.

Gatlin, however, has emerged as the greatest threat to Bolt's ambitions of winning a third consecutive clean sweep of the Olympic sprint medals - 100m, 200m and 4x100m - at Rio 2016.

Bolt's predecessor as Olympic 100m champion in 2004, Gatlin was unbeaten over both sprint distances last year, setting six of the seven fastest times for 100m and smashing his personal best for 200m.

The fact that he did all of this aged 32, when most sprinters are slowing down, and he was beating or matching times he set when he was proven to be cheating, has provoked widespread disquiet, bordering on disgust, on the international athletics circuit.

This flared up when the International Association of Athletics Federations (IAAF) proposed him for its Athlete of the Year award. German discus champion Robert Harting asked to be withdrawn from consideration in protest, while IAAF presidential candidate Lord Coe told the BBC he had"big problems" with Gatlin's nomination.

The Florida-based athlete, who was also booed by the crowd at London 2012, ultimately did not make the final shortlist, despite his undeniably impressive results.

Given this reaction, Nike is taking a risk in associating itself with Gatlin, who has never admitted to cheating, although it could be argued that all publicity is good publicity.

And with Nike locked in a fierce battle with Adidas, Puma and other challengers in the global sportswear market, the chance to sign a home-grown potential Olympic champion was clearly too good to pass up.