South Korea captain Son Heung-min will need time to re-adapt following his return from surgery to stabilize a fracture around his left eye, head coach Paulo Bento said after they held Uruguay to a 0-0 draw in their World Cup opener on Thursday.
Son, playing in a black protective mask, spearheaded the South Korean attack but did not have much impact as they had six attempts at goal but none on target.
Bento said the 30-year-old, who was injured midway through Tottenham Hotspur's Champions League match at Olympique de Marseille this month, joined the squad only in recent days.
"Son is a player who, up until his, injury, had continuous rhythm and good performance," Bento said of Son, who had five goals and two assists for Spurs this season before the World Cup.
"He had a serious injury, he was inactive for a considerable time. He joined the team only in the last few days.
"After an injury and being exposed to more aggressive games, it is natural it will take him some step to re-adapt."
Bento said South Korea had a better first half than the second because the quality of the Uruguay team, which includes veteran striker Luis Suarez and Liverpool's Darwin Nunez, shone through.
"I believe it was a great match in general, a match that was very competitive with a very high level of play. Two teams that respected each other," he said.
"We knew it would be a difficult game, we knew the quality of our opponents. They have players who are very evolved technically, very good physically and very experienced. This was a very good match from our side.
"We were suffering a little bit because they were very high-quality players ... but we conceded very little to our opponents."
The Portuguese coach said that the knock picked up by Kim Min-jae, who plays for Serie A side Napoli, also disturbed the team's defensive plans.
"I don't have enough data to make comments (about his injury). We will see what will happen," Bento said.
"Because of his injury, it hindered our performance as we could not continue the game as we had... We struggled to take our defensive lines to other areas and then decided to lower it and group them together.
"Min-Jae is a player who played almost all matches (in the Champions League for Napoli) in a short time and, as a consequence, we now have an injury in the World Cup."
South Korea, who are at their 11th World Cup, are level on one point with Uruguay in Group H. Ghana play Portugal later on Thursday.