D.C. United’s John Thorrington will miss at least one-quarter of the season with a knee injury. (Rob Carr/GETTY IMAGES)

The good news, if such a thing exists for D.C. United’s John Thorrington after being ruled out for two to three months Tuesday, is that the latest injury in a career of setbacks is straightforward: The medial collateral ligament in his left knee is severely sprained and he will miss at least one-quarter of the regular season.

Clarity, though, is a relief to Thorrington, who has been bedeviled by mysterious muscular conditions numerous times during a 13-year career.

“I know what I am dealing with and it’s not [related to] any past issues,” he said at RFK Stadium, his leg in a long brace and crutches at his side. “It’s easier to wrap my head around this one than the thoughts of, ‘Oh, not this again.’ ”

In the starting lineup for the second consecutive game Saturday, Thorrington was injured late in a 1-0 victory over Real Salt Lake. Alvaro Saborio was in the act of shooting when Thorrington stuck his leg in the way and took the full force of the forward’s follow-through.

“I don’t think he saw me and I went and blocked his shot but put my foot at the point of impact,” he said. “The lower half of my leg externally rotated with the ball on his foot.”

Thorrington, 33, left the match and underwent an MRI exam Monday. The results confirmed United’s initial suspicions. Given Thorrington’s history, United officials knew they would have to do without him for periods this year. But that mind-set had more to do with sore hamstrings, quadriceps and calves, not a knee ligament.

“It’s disappointing – it’s a big blow for us,” United Coach Ben Olsen said. “It was a fluke thing.”

Thorrington started in a three-pronged central midfield in his United debut at Houston on March 2 and in an attacking midfield role against Real Salt Lake.

About 15 minutes before departing Saturday, he was involved in the scoring sequence: A well-placed chip from distance forced goalkeeper Nick Rimando to make a leaping save, leading to Lionard Pajoy’s diving header.

With Thorrington out, Olsen indicated Marcelo Saragosa would partner with Perry Kitchen in the heart of midfield this Saturday against the New York Red Bulls in Harrison, N.J. Saragosa started in the opener and entered for Thorrington in the second game.

In the long term, Lewis Neal (currently sidelined with a strained groin) and Raphael Augusto (returning from knee tendinitis) will add central support.

“You lose someone who is very comfortable on the ball, very creative,” midfielder-forward Chris Pontius said of Thorrington. “He might not be the most athletic player, but he can find spots and get you the ball.

“You work so hard to get ready for the season and this happens in the second game. I feel bad for the guy.”

Thorrington joined United via MLS’s re-entry (free agent) draft in December after being released by the Vancouver Whitecaps. Among his many injuries, a knee ligament had not afflicted him since 2006.

An MCL sprain sidelined United captain Dwayne De Rosario last fall as well. He missed two months and returned in a limited role for United’s last playoff game. On Tuesday morning, Thorrington consulted with De Rosario about the rehab regimen.

“I have come back before, I know what it takes, and I will do it again,” Thorrington said. “There’s still a lot to play for this year.”

United notes: Dave Johnson and John Harkes will return to the broadcast booth when the club finalizes a local TV contract, a United official said. Assuming a deal is reached soon, the first local telecast would come April 5. (Before then, the next two games are on national TV.)