Federation of German Professional Boxers president Thomas Puetz has told German daily Bild that Soliman's urine sample tested positive for an undisclosed banned substance.
Puetz said a "difficult to detect designer drug with stimulating effects was found" following 39-year-old Soliman's unanimous decision win over Sturm in Dusseldorf on February 1.
No.1 IBF contender Soliman took to Twitter on Sunday to refute the claim and hint at legal action.
"Drug allegations are complete nonsense and an insult. Anyone who knows me knows my views about drug cheats," Soliman wrote.
"The matter is now in the hands of my lawyers & it will be pursued 2 the fullest extent possible. I won't be commenting further.
Soliman's manager David Stanley alerted his fighter to the report.
"He's absolutely gobsmacked because this (anti-doping) is a very important principle that he lives by," Stanley said.
Stanley, who is in the midst of negotiating a fight between Soliman and IBF middleweight world champion Daniel Geale later this year, said he had no official notification of a positive test.
"We understand this has all come out of the Sturm camp," Stanley said.
"I'm told that the Sturm camp is alleging that Sam has tested positive for an undetectable amphetamine, that's absolute rubbish.
"I'm also told that Sturm has identified who he should be fighting next so that he can then fight for the world title.
"This is an act of absolute desperation.
"I've contacted the Australian anti-doping commission to get them to get into contact with the German group because there are irregularities all over the place on this against someone who is vehemently opposed to any form of performance-enhancing drug use."
The Soliman camp insisted on drug testing before and after the bout.
"The reality of it is there is still unfinished business under our contract, because they did not comply with any of the testing points as in steroids," Stanley said.
"We went into that fight without that clause and it meant a lot of anguish in that last week.
Puetz said he would inform Germany's National Anti-Doping Agency and the IBF of a positive test.