American runner LaShawn Merritt, who has completed a 21-month doping ban, will return to the track in the 400m at Friday\'s Diamond League meeting in Stockholm, the organisers announced on Thursday. The 25-year Olympic and world champion over the distance tested positive for the anabolic steroid DHEA in three tests between October 2009 and January 2010. Last October an American Arbitration Association (AAA) panel declared that his ban would end July 27, less than the usual 24-month ban, thereby making Merritt eligible to compete prior to the world championships. The arbitrators stated they believed his positive test stemmed from an inadvertent action and was not intended to produce a competitive advantage. Merritt, who was not able to take part in the US national championships, was named in the US team last month for the world championships which take place in Daegu, South Korean in August.