Fleetwood Town's Gerard Kinsella has been banned from football for two years after testing positive for the anabolic steroid nandrolone.
The League Two midfielder, 21, admitted a Football Association charge after failing a drugs test in February.
His suspension, which is subject to any appeal, will run until February 2015.
Kinsella said the positive test came after his cousin twice injected him with a substance to relieve the pain of a shoulder injury.
The cousin, taxi driver Neil Kinsella, told an FA commission that he used the drug, Durabolin, himself as a painkiller and was not aware it was also known as 'nandrolone' - a performance-enhancing drug which reduces fatigue and promotes muscle growth.
The two injections took place at the player's home on consecutive days at the end of December 2012, shortly before he moved on a month's loan to non-league AFC Telford, where he played seven times and scored one goal.
The FA concluded that the former Everton trainee had been "significantly at fault" for failing the test, having determined he made "no proper efforts" to establish what the substance was and whether it was prohibited.
The two-year suspension has been backdated to 5 February, 2013 - the date on which Kinsella provided the positive urine sample at an 'out-of-competition' test.
Kinsella is yet to make a first-team appearance for Fleetwood, who have said they will make a statement "in the fullness of time". He has a year remaining on his contract at Highbury.