As has been reported, Evan Gattis underwent surgery to repair a hernia and is expected to miss four to six weeks. This is something that he says has been bothering him for some time. Which begs the question of how long and to what extent has it affected him? And, if it was affecting, will that affect his performance moving forward? If not, will the surgery have implications on his performance.
To answer this, you have to get down to what exactly the problem was anatomically. In general, a hernia is simply a tear in the abdominal wall allowing for the contents to push past the wall into the leg, thoracic cavity, or space between the wall and the skin. Hiatal hernias are a tear in the diaphragm causing lots of indigestion and other complications because stomach acids are able to work back up the esophagus more easily. Umbilical hernias are tears right at the navel and can allow the intestines to protrude. Same with femoral hernias. Inguinal hernias are where the sexual organs drop from the abdominal cavity and allow the intestines to drop as well.
Here's the twist. A sports hernia isn't actually a hernia. And Gattis had a sports hernia. This "hernia" is actually a strain of the abdominal or groin muscles that attach to the pubic bone or a sprain of the tendons or ligaments attached to that same area. Eventually it can lead to a real hernia because of changes in movements that stress the abdominal wall.
These "hernias" come from lots of forceful twisting. That pulls on the groin muscles and the abdominal muscles resulting in the strains. The strain creates an imbalance between the groin and the rectus abdominis. The imbalance over time gets worse due muscle tightness/spasms/weakness. Rest will usually make them better but unfortunately will come back. Conservative measures focus on improving flexibility and strength of the core muscles and hips. But, eventually it doesn't work and surgery is a last resort.
Surgery consists of releasing the muscle contracture, cleaning up possible scar tissue, and repairing any tears. If there's a real hernia as well, the surgery will also repair the tear in the abdominal wall.
Recovery depends on if there was a real hernia or not. With a real hernia, rest is a part of the early phases to limit increases in intra-abdominal pressure from exertion with activity. However, in the absence of a real hernia activity can begin much sooner. The focus is on flexibility of the groin and rectus abdominis and improving the muscle strength balance. With that accomplished, working on movement patterns to ensure proper hip and lumbar mobility is achieved. Then progression through more rigorous activities and on to sports activities.
If all done properly, it shouldn't be a lingering problem. In fact, because of improvements in mobility and muscle balance can actually improve core stability. With improvements in those areas, the legs and arms can perform better. That doesn't mean better baseball performance. Just better movement.
TL;DR: Dude's gonna be fine.