The Impact (10-5-5), who ended a five-game winless run with a 1-0 win over first-place Kansas City in extra time in their last outing, will face D.C. (2-15-4) on Saturday night in their first MLS meeting of the season.
D.C. has the worst record in the league, but Impact captain Davy Arnaud knows that the squad led by Canadian international Dwayne De Rosario still has talent.
"It is dangerous," Impact captain Davy Arnaud said. "D.C. has good players.
"I don't know if they are mathematically out of the playoff picture (they aren't), but they're pretty much out of the playoff picture. So if you have a team that's playing with nothing to lose, and if they've lost a lot of games and they're playing looser, that can be dangerous."
United has taken a stunning fall this season after finishing second in the Eastern Conference in 2012. Most of it comes from a sudden inability to score goals. They have only 10 on the season, despite having most of their top players back.
Luis Silva has scored twice since he was acquired from Toronto FC on July 9 and that ties him for the team lead with De Rosario and forward Lionard Pajoy.
Injuries have become a problem, as Pajoy underwent hernia surgery this week and will be out for more than a month. They may also be missing midfielder Chris Pontius, who has sat out the last two games with a hamstring injury.
But they will have goalkeeper Bill Hamid back from duty with the U.S. squad that won the CONCACAF Gold Cup. Hamid did not play in the tournament.
D.C. is 0-4-1 since its last victory on June 22, a 1-0 decision at home against San Jose.
Their only other win was also at home, again against a strong opponent as they beat Real Salt Lake 1-0 on March 9.
So the Impact are on alert.
"This will be as tough as any road game because they don't want to lose every game," added Arnaud. "I've played in a lot of these games where it looks like it should be a result and sometimes it's not."
The Impact will be looking to get its attack on track. They appear to have solved the defensive woes they encountered at the start of their winless run, but the attack has been anemic. Rookie Blake Smith's 96th minute goal against Kansas City was their first in three games.
"That was a huge win, just for morale purposes," said fullback Jeb Brovsky. "When that goal went in we felt like a monkey came off our backs."
They will likely be missing central defender Alessandro Nesta, who didn't practise this week due to a sore leg, so Hassoun Camara may move into the middle from right back.
The new signings, centre back Adrian Lopez and midfielder Hernan Bernardello, are not likely even to make the trip to D.C., but may start seeing action next week as CONCACAF Champions League play opens with a visit from the San Jose Earthquakes.
Striker Marco Di Vaio, who leads the team with 11 goals, and midfielder Patrice Bernier each played a half of the MLS all-star game on Wednesday night but should be fit to face D.C.
It is the start of a busy week and a busy month for Montreal. They will play at Chicago three days after San Jose. They have seven games in August, including two in the Champions League.
That will test their depth.
"It's in the back of our heads that we want to do well in that competition," said Brovsky. "A lot of guys who haven't been getting a lot of minutes are licking their chops because they see that as their opportunity.
"With Wednesday and Saturday games, we don't know what the lineup's going to be because they'll be calling on a lot of guys and everyone will get their shot. It's going to be a wild month of August."
Forward Andrew Wenger will miss the start of it with a broken toe. He tried to play through the injury, but said it got too painful. He may be out for two or three weeks.