Tillman signed a 10-day contract via hardship exemption with the Hawks on Tuesday.
Tillman was averaging 13.1 points and 7.5 rebounds across 22.0 minutes per game for the G League College Park Skyhawks. Atlanta currently has 13 players out due to COVID-19 protocols, so the 25-year-old power forward will likely be thrust right into game action during Wednesday's rematch with the Bulls.