02/23/2015 02:23 EST | Updated 04/25/2015 05:59 EDT

New-look Impact faces first real test in CONCACAF quarter-final in Mexico

The new-look Montreal Impact is about to get its first real test.

The Impact, with new faces on defence and at midfield, will try to shake off winter rust and adapt to the thin air in Mexico when they face Pachuca on Tuesday night in the opening leg of their CONCACAF Champion's League quarter-final.

"We're as ready as we can be," assistant coach Mauro Biello said this week. "We've tried to acclimatize to the weather and the altitude.

"And with a lot of new faces, we did a lot of playing and working on our defensive shape."

The Impact hope to keep the score close in the away leg and try to win the two-game aggregate goals series in the home leg March 3 on artificial turf at Olympic Stadium.

Pachuca will have the advantage of being in mid-season form, while Montreal, which has its off-season in the winter, will be in its first match of the 2015 campaign.

The Impact opened camp Jan. 23 in Montreal and have been in Mexico since Feb. 8, where they played three exhibition games.

It wasn't much time to build cohesion on a team that made several changes after finishing last in Major League Soccer last season.

A new central defence partnership of Belgian Laurent Ciman and former Chicago Fire defender Bakary Soumare is expected to start behind two new holding midfielders in Nigel Reo-Coker and Marco Donadel.

A plus for Montreal is that star midfielder Ignacio Piatti, returning from off-season knee surgery, is fit to play. Veteran midfielder Justin Mapp is also fine after missing time early in camp, but there are doubts injured midfielder Andres Romero will be ready.

Altitude will be a factor at Pachuca, about 90 kilometres from Mexico City. The thin air tends to leave visitors short of breath, and coach Frank Klopas will need to monitor his players and use his substitutions wisely.

"It's a big deal," said Biello. "They say you never really acclimatize to it.

"You make a long run and it takes a bit more time to recover. That's what slows you down. But all the players say they feel better than they did the first week here. It's an advantage for (Pachuca), but hopefully we'll have the advantage when we get to Montreal and play on (artificial) turf and it's minus-40 outside."

Pachuca is not considered a high-scoring club, but Biello said they are quick on the flanks with young wingers Jurgen Damm and Hirving Lozeno.

It remains to be seen what lineup the Mexicans put on the field after using their first team in a 2-1 win at home in league play on Saturday. Pachuca has another league match Friday before heading to Montreal.

"We know it's a difficult game against a good opponent," said Biello. "We worked on our team shape and defending. If we can execute our strategy, we have a good chance

It is Montreal's second time in the CONCACAF quarter-finals.

In 2009, when they were playing in a lower league, they had perhaps the best moment in their 22-year history when they won the opening leg 2-0 over Santos Laguna before 55,571 at the Big O before collapsing late in 5-2 defeat in Mexico in the return leg.

Qualifying for the Champions League was one of the few bright spots in a 2014 season in which they won only six of 34 league games and didn't win at all away from home.

The Impact open the MLS regular season March 7 away against D.C. United