The 29-year-old is among three players including compatriot David Accam who are being considered for the draft-trade.
C.J Sarpong, a Ghanaian-born American forward scored four goals in 33 appearances for Union last season.
The forward signed a contract extension with Union until 2019 with an option for a further year.
Sapong originally entered MLS as the 10th overall pick by Sporting Kansas City in the 2011 MLS SuperDraft.
Over four seasons in KC, the Manassas, Virginia native and James Madison University product helped Sporting win the 2012 US Open Cup and 2013 MLS Cup before moving to Philly in a 2015 trade.
Since then he has scored at least seven goals in each of his three seasons with the Union.
Internationally, Sapong has registered four caps with the US national team.