The Montreal Impact cannot be blamed for moving Tuesday’s first leg of the MLS Eastern Conference to the Olympic Stadium. With triple their usual fans in the building, the it’ll certainly have a big-game feel. The 60,000-plus fans will pad Montreal’s ticket revenue, and they’ll be nice and warm in the domed stadium.

What IMFC may not explicitly mention, though, is the tactical advantage the team draws from the synthetic turf surface on which they’ll host Toronto FC.

The Big O’s pitch is notorious for baffling opposing teams. Montreal have beaten some strong competition in the CONCACAF Champions League in that venue, most recently CF Pachuca and Alajuelense in 2015. The turf is set over a concrete slab, which makes it extremely bouncy and unforgiving.

According to Impact keeper Evan Bush, it’s not even consistent.

“It’s not only certain areas where it’s hard and there’s concrete under it, there’s certain areas that are hollow,” he told the Montreal Gazette. “I’m not sure if there’s like trap doors under there or what happened. But maybe (former Montreal Expo) Moises Alou is hiding under there somewhere under a trap door. I don’t know?”

The stadium’s pitch received a facelift for the 2015 Women’s World Cup, with a new technology known as Xtreme Turf installed, but it has since been returned to the previous, more basic surface.

The unpredictability of such a field can slow down Toronto’s attack, and we’ll likely see a fair amount of wonky passes when players misjudge the pitch. Worse still, a hard surface like Montreal’s can wreak havoc on players’ knees and ankles. It would be disastrous for TFC if someone like Sebastian Giovinco or Michael Bradley were to get hurt.

Only five teams in MLS still regularly play their home games on artificial turf: Vancouver, Orlando City, Seattle, New England, and Portland. Of them, TFC have played away to all but Seattle this season. The Reds struggled on their synthetic fields , posting a 1-3-1 record and a -2 goals differential, despite all four opposing teams missing the playoffs this year.

Compare that to Toronto’s 6-4-5 away record on grass this year, where they’ve scored 22 times and conceded just 15, and you can see why Montreal’s players may not be too bothered about having to play on the unpredictable turf.

The Impact have played at Olympic Stadium twice already this year, going indoors for their first two home matches. They beat some quality competition, first knocking off New York Red Bulls 3-0 and then defeating Columbus 2-0. They’ve also played six away games on turf this year, with a 2-3-1 record—hardly better than TFC, but still an extra game’s experience with the surface.

On the other hand, Montreal have the worst points percentage at home of any MLS playoff team, securing just 51% of the available points from their 17 home league games this year. Of course, playing in front of three times the usual amount of fans may extend their home field advantage, but an estimated 1500 or so Torontonians are also expected to be there.

To prepare for the difficult playing surface in Montreal, Greg Vanney has had his team training on turf this week. However, the main domed pitch at TFC’s Kia Training Complex is reportedly too good to prepare them for the Olympic Stadium. Vanney has instead had the Reds practising on one of the complex’s outdoor synthetic field, which is in worse condition and therefore is closer to the Big O’s turf.

Vanney confirms what we saw this week: team training on worst turf at KIA. Turf in the main bubble is too good to replicate Big O. #TFCLive pic.twitter.com/afFmIqRmmv — Gareth Wheeler (@WheelerTSN) November 18, 2016

At the end of the day, no matter the advantage it gives Montreal, the field at Olympic Stadium will drag down the quality of play in a game that has the potential to fling soccer into the mainstream in Canada. The MLS product will be damaged if this game is decided by a wonky bounce or a freak injury to a key player on the foreign surface.

Obviously a 60,000-strong crowd on a weeknight is almost a perfect storm for the growth of Canadian soccer, but the game has to attract new supporters. Casual fans tuning in on TV may not be impressed if the level of play is below the usual standard between these two teams.

Note: The original version of this article stated that a new type of turf had been installed for the 2015 Women’s World Cup. This turf has since been removed and the article has been updated accordingly.