SOCHI, Russia (Reuters) - Poland will make changes for their match against Colombia and start “more aggressively” in what will be a key match against opponents who also lost their opening contest, striker Dawid Kownacki said on Thursday.

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Both sides were defeated 2-1 in their first Group H games -- Poland at the hands of Senegal and Colombia to Japan -- meaning another defeat is unthinkable for either of them.

“We have to play more aggressively,” Kownacki said. “In the Senegal match, we did not show the aggression, we did not attack the rival as we should have. We should have played sharper. This was a key mistake.

“This (aggression) will be important in the match with Colombia. We have to get close to them, they have great players, a lot of individuals who can do a lot when they have control of the ball.

“When we get possession we need to make faster decisions. We kept the ball too long with Senegal, we could not get into the rhythm.”

Assistant coach Hubert Malowiejski said some of those who disappointed against Senegal would be dropped but he did not name names.

“There will be certainly be changes, it is not very likely that we will play with Colombia with the same players,” Malowiejski said.

“How many changes, and which positions, this decision has not been made yet. We have training sessions ahead of us, especially today’s training. The skeleton of the team will remain the same but there will be changes.”

The results in Group H have been one of the most surprising in the World Cup with the underdogs winning both opening ties.

That makes Sunday’s game in Kazan a crunch match for both sides, especially as Senegal play Japan a few hours before.

Kownacki, however, sought to introduce a note of calm.

“This tournament has just started and after the first match not all is lost,” he said.

“We lost one match but there are two ahead of us, it is all up to us. We know how to play football, everybody knows that, we are used to beating better rivals. All we need to do is show it again.”