Union’s Quinn Sullivan says he suffered a torn ACL in Saturday’s game

The Union’s young midfield star Quinn Sullivan announced Monday evening that the injury he suffered in Saturday’s win at D.C. United was a torn ACL.

“Well … this is a message I hoped never to write,“ the 21-year-old said in an Instagram post. ”I am gutted to not be able to finish this incredible season with the guys, but really proud to be a part of this team. I have full confidence that this special group will lift a trophy. Let’s win it @philaunion."

It has not been confirmed which knee he injured, nor is it clear exactly when it happened. But there’s a definite candidate.

In the sixth minute, Sullivan fell to the ground awkwardly after colliding with D.C.’s João Peglow as they hustled for a loose ball. He kept playing, then a few seconds later he fell again after pursuing Peglow a second time. At that point, he sat on the ground, raised a hand — the universal signal to ask for help — and grabbed his right knee.

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A few more seconds passed, and Sullivan got back up and tried to jog. He could not, and sat back down. The ball was far away, and the rest of the players didn’t see him, so play continued until the ball went out. Then the Union’s medical staff went onto the field.

Sullivan jogged off under his own power with the staff, and tried on the sideline to overcome what he must have presumed was a lesser injury. But he could not, and the staff had to help him to the locker room. Sullivan’s frustration was seen on the TV broadcast as he headed away.

Sullivan had three goals and eight assists in 31 games for the Union this year.

The injury leaves the Union without not just one of their most creative players this year, but without a big piece of their midfield depth chart. Milan Iloski and Indiana Vassilev will likely be the starters the rest of the way, with Jeremy Rafanello and Cavan Sullivan first off the bench. Ben Bender and C.J. Olney would be behind them.

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Of those four, Cavan Sullivan — who turned 16 on Sunday — could see the biggest impact. Along with getting more first-team minutes, Quinn’s youngest brother is a major candidate to play for the United States under-17 men’s national team at that age group’s World Cup in November in Qatar.

But the tournament takes place during the MLS playoffs, and club teams aren’t required to release players to youth World Cups. So the Union might decide to keep Cavan here.

Cavan has dealt with his own injury recently, a groin tweak that he suffered playing for the Union’s reserve team Sept. 21. He didn’t practice most of last week, and though he returned to the field Friday, the club chose prudence and held him out of the reserve team’s game Friday and the first team’s trip to D.C. Saturday.

He took to Instagram after Quinn’s announcement and said: “Finishing out this season for u” with a heart emoji.

The Union have two games left in the regular season, Saturday’s home contest with New York City FC (7:30 p.m., Apple TV) and the finale Oct. 18 at Charlotte FC.

If Inter Miami drops points on Tuesday at home against the Chicago Fire, a Union win Saturday could clinch first place in the Eastern Conference and the Supporters’ Shield trophy for the best regular-season record leaguewide.