The Argentine coach has the luxury of going into the game on Tuesday in Cuiaba having already qualified for the last 16 after impressive wins against Greece and Ivory Coast in Group C.

Pekerman said he had to weigh up the advantages of giving established players a rest and letting others have a run out with keeping a sense of continuity.

"We have trained with all the players. We have tested many players and we have considered many possible changes but I won't confirm until tomorrow who will play," he said.

"There might be some changes compared with the last match but I haven't decided exactly how many changes," he added.

The former Argentina coach said even with new names, the team would try to play the same pacy football that has yielded a 3-0 win against Greece and a 2-1 victory against Ivory Coast.

The coach said it was an advantage to have qualified with a game to spare but he did not underestimate the challenge from Japan, who have disappointed in Brazil so far, taking just a single point from two games.

"From the beginning we thought that our group was very balanced. We didn't think that one of the teams would have qualified already during the first two matches but fortunately we were able to do so," said Pekerman.

"Tomorrow we will play one of the most dangerous teams in our group. We always thought they would be very difficult opponents."

Midfielder Fredy Guarin said the players were fully focused on Japan, refusing to look ahead to any potential clashes in the knockout rounds.

"We think it's going to be a very difficult match," he said. "We're taking it very seriously. We know that Colombia have already qualified for the next round but still it's a World Cup game."

Colombia, ranked eighth by FIFA, are making their first appearance in the World Cup finals since 1998. Their last-16 showing in Italy in 1990 was the only time until now they have made it out of the group stage.

The side are missing Monaco striker Radamel Falcao through injury but his club team-mate James Rodriguez has shone in his absence, scoring twice so far.

Pekerman said Falcao was a big loss but praised his team for reacting in a positive way.

"For me as a coach this proves that my players are very well prepared and have a very strong character," he added.

Colombia have six points, with Ivory Coast second on three points. Japan and Greece both have a single point, though the Europeans have an inferior goal difference.

Ivory Coast play Greece in the other Group C match on Tuesday in Fortaleza.