Class is back in session.

“The Professor” Kyle Hendricks is returning to the Cubs rotation for Sunday’s series finale in Pittsburgh, manager Craig Counsell said Saturday evening. Hendricks was officially activated Sunday morning from the 10-day IL, with RHP José Cuas being optioned to Iowa to make room on the active roster. 

Hendricks, 34, was initially scheduled to make another rehab start with Triple-A Iowa Sunday but a minor back issue for Jameson Taillon has shifted the Cubs’ rotation needs.

[WATCH: Taillon updates his health status]

Taillon’s regular turn in the rotation was Friday but was pushed back. The Cubs hoped he would be able to take the ball Sunday but they want to give him a couple extra days.

Hendricks, meanwhile, went on the IL on April 22 with a back injury of his own.

He was off to a really tough start to the year with an 0-3 record, 12.00 ERA and 2.10 WHIP in 5 starts. That includes 8 homers in 21 innings after he permitted only 13 homers in 137 frames last season.

After an initial period of rest for a few days, Hendricks began throwing bullpens to help get his mechanics back on track.

He made a pair of rehab starts, first with Double-A Tennessee and then again with Iowa last week. In those minor league outings, Hendricks had a 2.89 ERA and 1.50 WHIP while striking out 13 batters in 9.1 innings.

Cuas, 29, pitched 2 scoreless innings in Saturday’s loss to Pittsburgh.