Gregus will spend the next year at the Reebok Stadium with a view to a permanent deal.
“Jan is a very talented player who I have monitored for a while now,” boss Dougie Freedman told Wanderers’ official website. “We’ll have a closer look at him now and see how he gets on.”
Earlier on Friday, Bolton secured the services of West Brom defender Craig Dawson on loan until the end of the season.
Scoring against Celtic was the best feeling Josh Windass has ever experienced and the Rangers forward is hungry for more goals.