Belgium striker Romelu Lukaku admits his team were given a "reality check" with their 2-0 loss to Italy at Euro 2016 on Monday.
Goals from Emanuele Giaccherini and Graziano Pelle saw Italy to their surprise win in the Group E clash.
Ranked second in the world, Belgium were considered among the pre-tournament favourites - but they failed to live up to that in their opener.
Lukaku said the loss would bring Marc Wilmots' team back down to earth.
"We have both feet on the ground now. We know what we have to do now," he told The Guardian.
"A lot of people were talking before the tournament about what we can do but we had a reality check against Italy and sometimes that's good to know you still have a long way to go.
"We played against a team that is known for being tactically very strong, very efficient and that's what we have to learn.
"If you want to become a big nation sometimes you have to deal with setbacks. We have to move on, become stronger, work even harder than we did, play well and win the games."
Lukaku warned his team just how important their next outing - a clash against the Republic of Ireland on Saturday - was.
The Everton star is also wary of what Martin O'Neill's men are capable of, saying: "We have to win against Ireland now and we have to play good football as well.
"Ireland has a good team. Defensively they're very good and up front they have players who can make a difference.
"They've got a lot of experience with Robbie Keane and Shane Long and [James] McClean from the left can make a difference so it's going to be difficult and we have to be wary of that."