On February 21, 2017, Callahan signed with Russian side Parma of the VTB United League.
[4] On July 19, 2018, Callahan signed a one-year deal with Donar, defending champions of the Dutch Basketball League (DBL).
[8] On December 24, 2019, after a small stint with Balkan Botevgrad in Bulgaria,[9] Callahan returned to Greece for Ionikos Nikaias.
[10] On March 10, 2020, Callahan received a four-year ban from FIBA competitions after a 2019 doping control test came back positive.
The two bags, containing an AK-47 assault rifle and a Taurus .38 special, were found hidden underneath nearby leaves.