McLaren is set to use a sixth driver of the 2024 IndyCar season as Alexander Rossi has been ruled out of this weekend’s race in Toronto after breaking his thumb in practice.

Rossi, who is leaving the team at the end of the season, crashed at the Turn 8 right-hander late on in practice for this weekend’s street course race.

While the crash was at low speed, Rossi kept his hands on the steering wheel turning trying to avoid the impact, and you can see the harsh swivel of the steering wheel caused by hitting the wall while he's still holding the wheel.

"It's unfortunate because the injury occurred when I almost made it around the corner and I didn't want to give up on it, so I didn't quite get my hands off the wheel in time," said Rossi, who is eighth in the points standings.

"However, everyone seems optimistic about the kind of injury it is. We're going to take the next steps here and get ready for Gateway [the next IndyCar race].”

While no timeline on a recovery has been outlined, Gateway takes place in four weeks' time on August 15.

More pressingly for McLaren, it faces a race against time to replace Rossi for what will be a single practice session before whoever takes over the #7 car then goes into qualifying.

The team’s sporting director Tony Kanaan was rumoured to be an option to replace Kyle Larson at the Indianapolis 500 (in case it rained and Larson had to skip the race) and Kanaan is on site in Toronto and could be the team’s best and only realistic option.

McLaren could look further afield but is running short on time.

Team principal Gavin Ward said he was "gutted" for Rossi and that McLaren would do "everything we can to support him".

McLaren is no stranger to IndyCar replacement drivers this year.

Its 2024 signing David Malukas failed to make a start for the team after a pre-season injury kept him out until June, by which point McLaren had released him. It chose to sign Theo Pourchaire to replace him instead, and then subsequently dropped Pourchaire mere races later in favour of Nolan Siegel.

Callum Ilott also stood in for Malukas for two races.

Rossi's replacement isn't the team's only concern in Toronto, as Pato O'Ward - who is on a brilliant run of form that has catapulted him into third into the championship entering this weekend - had an issue with what the team said was the hybrid coolant pump during first practice.

The team is also mourning the death of O'Ward's spotter, Bob Jeffrey, to cancer ahead of this weekend. He had also worked with the likes of Tony Stewart and Josef Newgarden.

Jeffrey was a champion spotter in IndyCar, the IMSA SportsCar Championship and NASCAR, and the team is running special stickers in his honour - and has also placed his headset where its spotters will work from this weekend.