Indianapolis Colts quarterback Andrew Luck's treatment and rehab of his surgically repaired right shoulder is apparently going well, but when he resumes throwing in the near future will determine whether he needs corrective surgery in January to address the setbacks that unexpectedly sidelined him for the 2017 season, sources told ESPN.

Luck is optimistic he can avoid another surgery based on the results of his extended European treatment and rehab, sources said. He is scheduled to return from his trip in the next week.

The next stage is for Luck to engage in a throwing regimen that previously resulted in a setback, with pain and discomfort in the same throwing arm that underwent surgery in mid-January to repair a torn labrum. The specific pain Luck previously experienced was attributed to biceps tendinitis, sources said.

If the pain returns during the throwing stage, an urgent discussion will occur for Luck to undergo a corrective surgery that involves relocating the biceps tendon that is attached to the repaired labrum, sources said.

Andrew Luck intends to test his throwing arm before deciding whether he needs to undergo an additional surgery, sources told ESPN. AP Photo/AJ Mast

In the procedure known as a tenodesis, the biceps tendon is reattached by a screw to the humerus, the long bone of the upper arm that connects the shoulder and the elbow.

The normal recovery from the tendon procedure ranges from three to six months, according to medical sources, and would not normally project as a surgery that would threaten the 2018 season.

The Colts and Luck have been aware of the possible corrective surgery when he sought multiple opinions after his setback that ultimately resulted in the team placing him on injured reserve Nov. 2. Luck chose the conservative path with treatment and rehab in Europe, sources said. The latest information has been encouraging but without the benefit of throwing the football.

Luck ultimately would have the final say on whether he would have surgery if the pain returns, but the Colts would enter the offseason with uncertainty at the position they thought they had secured when they made Luck the No. 1 pick in the 2012 draft and subsequently signed him to a $122.9 million contract extension in June 2016.