Joe Ross to undergo Tommy John surgery on Wednesday

CINCINNATI - The MRI arthrogram performed on Joe Ross' right elbow confirmed a "full-thickness tear of the ulnar collateral ligament," Nationals general manager Mike Rizzo said Saturday afternoon, and the right-hander will undergo Tommy John ligament replacement surgery Wednesday in Texas.

"I think we knew (based on) the MRI it was going to be serious," said Rizzo. "Obviously, you don't know to what degree and the (MRI) arthrogram made it very clear what happened to him."

Manager Dusty Baker didn't have details about Ross' prognosis past the scheduled surgery, but intonated that the damage found in both the MRI and MRI arthrogram was extensive.

"He had some complications from the past," Baker said, adding that Ross has been shut down with an elbow injury while in high school, something the manager wasn't aware of previously. "It's kind of ugly in there."

Dr. Keith Meister will perform the surgery in Arlington, Texas, said Baker, and Ross will recover and rehab with his brother, Tyson, a Rangers pitcher who has battled back from shoulder problems to take a place in the Texas rotation.

"I think that's going to help him psychologically to be around family and somebody that's had some of kind of procedure," Baker said.

Joe Ross sat quietly on a chain in the visiting clubhouse at Great American Ball Park on Saturday, a stimulation device attached to his arm in an effort to reduce inflammation and swelling before the Tommy John procedure, which could sideline him for 12 to 18 months.

Ross met with Baker on Saturday afternoon, and Baker said the 24-year-old took the news about as well as could be expected.

"We had a long conversation today and I told him that he has to go in with a positive outlook," Baker said. "The first one's always tough, and I told him I had a number of them. You got to be in a proactive versus reactive (mindset) and you have to go into things with a positive outlook. ... I told him to talk to a couple of guys here who have had this procedure before, which helps. Mainly (Matt) Wieters and Stras (Stephen Strasburg). So it's always tough on the first one. But I know a whole bunch of guys who have come back better and thrown harder and quicker with better mechanics."

With Ross sidelined at least until the midpoint of next season, and perhaps longer, the Nationals' immediate need is to figure out who will take the next turn in the rotation where a fifth starter is needed, on Tuesday in Anaheim against the Angels.

It's likely the Nationals will at least go with internal options, though who exactly that will be isn't known. With the July 31 nonwaiver trade deadline nearing, the Nationals could also seek a deal for a back-of-rotation starter to get them through the season.

"We haven't gotten that far yet," Baker said. "It depends on how well internal does in his absence. That's going to determine needs."