Wheeler had a successful right upper extremity blood clot removed on Aug. 18, and during the evaluation and second opinions, it was recommended that he undergo surgery, which will take place at a later date.
According to the Mayo Clinic, venous thoracic outlet syndrome is a group of conditions in which there’s pressure on blood vessels or nerves in the area between the neck and shoulder, which can cause numbness in the fingers.
The team said that the recovery from the injury will likely take six to eight months.
Wheeler, a three-time All-Star, was placed on the injured list earlier in the week and last took the mound last Friday, throwing 97 pitches against the Washington Nationals.
The 35-year-old Wheeler was having an outstanding season for the first-place Phillies, going 10-5 with a 2.71 ERA in 24 starts over 149 2/3 innings with 195 strikeouts.