Effross will make spot start Tuesday against the White Sox in place of Drew Smyly, who was placed on the bereavement list, Tim Stebbins of NBC Sports Chicago reports.
Effross has exclusively pitched out of the bullpen thus far in his major-league career, posting a 2.92 ERA and 30:2 K:BB in 24.2 innings of relief over the last two years. He's never recorded more than six outs in a big-league appearance and was almost exclusively a reliever in the minors, so Tuesday's game will likely be a true bullpen day.