The OMG singer, 32, believes the tape could be one of the items that was stolen from his car during a robbery in 2009, according to TMZ.com.
In December 2009 Usher reported $1 million worth of belongings were stolen from his car, including two laptop computers and jewellery.
Sources close to the singer told TMZ they believe the X-rated tape may have been among the stolen items.
The celebrity website was sent a clip of the alleged tape and confirm that it is indeed Usher and Foster, 40.
It is not clear when the tape was recorded during their three-year relationship.
The couple married in August 2007 after Usher became romantically involved with Tameka, his then-stylist, in 2006.
They have two children together, Usher Raymond V, three, and Naviyd Eli Raymond, two.
He filed for divorce in June 2009, citing irreconcilable differences, claiming they had lived apart for over a year.
The couple’s divorce was finalised in November 2009.
In February that year Foster was placed into an induced coma after suffering a cardiac arrest in hospital in Brazil, as she prepared to undergo liposuction.
Usher is currently on his OMG world tour, and will perform dates across Australia this week, before heading to New Zealand and back to the US.