(CNN) -- Ivan Klasnic's second-half goal made it three victories out of three for Group B winners Croatia, as they beat Poland 1-0 in Klagenfurt to ensure an early exit for their opponents.
Klasnic celebrates his goal as Croatia maintained their 100 per cent record in their 1-0 victory over Poland.
Klasnic struck in the 52nd minute to earn a much-changed Croatian side a deserved victory and continue their impressive start to the tournament, which has also included triumphs over Austria and Germany and will next see them take on Turkey in the quarterfinals.
They will do so without defender Dario Knezevic who suffered knee ligament damage when he collided with goalkeeper Vedran Runje early in the game.
Croatia coach Slaven Bilic said that 26-year-old Knezevic, who has eight caps, is "99 percent out of the championship."
"It is a big blow for us, as he is one of our main defenders," Bilic said.
Team doctor Zoran Bahtijarevic said it was unclear when Knezevic would return to play. "It is lucky that he did not break anything," Bahtijarevic said
For Poland, the unlikely task of claiming a last eight spot proved mission impossible.
Needing a win and a favorable result from the Austria-Germany game to continue their adventure in their first European Championship finals, they could find no way through against an impressive Croatia.
It was pretty much all Croatia after that in terms of goalscoring chances in the opening 45 minutes, with Slaven Bilic's new-look side getting in behind the Polish defense on a number of occasions.
The first time came in the 14th minute when Danijel Pranjic was played through by Klasnic, but the left-back's attempted chip over Poland goalkeeper Artur Boruc drifted harmlessly across goal.
Bilic's side went much closer with their next opportunity, when Hrvoje Vejic's glancing header from an Ivan Rakitic free-kick bounced just past the far post with Boruc a helpless bystander.
Boruc was needed to save his side in the 31st minute though when Klasnic was played in on the edge of the area, and the Celtic goalkeeper did well to come out and block the Werder Bremen striker's shot.
Croatia continued to push for the opener right up to the break and Jerko Leko sent a low 20-meter shot fizzing just wide of Boruc's right post, before the Polish number one did superbly to save from Klasnic on the stroke of half-time following another one-on-one with the Croatia hitman.
Croatia may not have got the breakthrough their play deserved in the first period, but they needed just seven minutes of the second half to take the lead.
The goal involved two of the game's most impressive performers, with full-back Pranjic racing onto a loose ball on the edge of the Poland area before cutting a pass back to Klasnic, who slotted home first time low to Boruc's left.
It marked a personal milestone for Klasnic, who has resurrected his career to become the first player to recover after having a kidney transplant.
With Germany also taking an early second-half lead in Vienna, Klasnic's strike all but signalled the end of Poland's slim qualification hopes but they continued to battle and the hard-working Jacek Krzynowek fired in an effort that went wide of the far post.
At the other end Pranjic almost caught Boruc out with a cross that landed on the top of the crossbar, before Poland had arguably their best effort up to that point through Roger Guerreiro.
The Brazilian-born forward picked up possession inside the Croatia area, but his low shot in the turn beat everything -- including the far post.
Guerreiro, who has impressed for Poland in this tournament, caused more problems for the Croatia defense in the 68th minute when his far-post cross picked out Marek Saganowski, but the striker's downward header was well held by Runje.
Poland's defense were given a boost with 17 minutes remaining when Bilic opted to replace the dangerous strike pairing of Klasnic and Mladen Petric, but that did little to help Leo Beenhakker's side at the other end of the field.
Polish substitute Ebi Smolarek had two decent efforts for his side in the closing stages but neither were on target, before Tomasz Zahorski missed a gilt-edged chance in the 88th minute when, after going clean through, he was denied by the feet of Runje as Croatia held on for the win.