NFL players will have a blood sample taken during training camp physicals as part of a population study for human growth hormone in order to determine the threshold for a positive test, the NFL Players Association's board of directors said in a memo sent to players Monday that was obtained by ESPN senior NFL Insider Chris Mortensen.

The NFLPA board said in the memo that "several additional issues" need to be resolved, including the "issue of discipline" before an agreement with the NFL on HGH testing is reached and a proposal is brought to the players for a vote.

A source, meanwhile, told ESPN NFL Insider Adam Schefter that even with the population study, "No one will be suspended for HGH use in 2013."

The blood sample will only be used for the HGH population study, the memo states. Dr. Alan Rogol has been commissioned by the NFL and NFLPA to oversee the study.

The labor agreement that ended the NFL lockout in 2011 allowed the league to test players for HGH -- once the union approved the process. The NFL Players Association has said it favors testing, but has reservations about the appeals process.

Supplemental HGH is a banned substance that is hard to detect and used by athletes for what are believed to be a variety of benefits, whether real or only perceived -- such as increasing speed and improving vision.

Among the health problems connected to HGH are diabetes, cardiac dysfunction and arthritis.

NFL spokesman Greg Aiello told The Associated Press that the discussions between the league and the union regarding HGH testing are focused "on a full resolution of any remaining issues."

Information from The Associated Press was used in this report.