South Korea men's national football team head coach Shin Tae-yong said Thursday that its two recent friendly matches in Europe have boosted their preparations for the 2018 FIFA World Cup.

Shin returned home after suffering consecutive defeats in their World Cup warmup matches against European opponents. South Korea fell 2-1 to Northern Ireland last Saturday and lost 3-2 to Poland three days later.

Despite the losses, Shin claimed that the two matches gave them a big help for their World Cup preparations.

"Against the world's 24th-ranked team (Northern Ireland) and sixth-ranked (Poland), we showed good performances," Shin told reporters after arriving at Incheon International Airport, west of Seoul. "We found out our problems by looking at the situations in which we conceded goals, so this will help us to prepare well for the World Cup."

In both friendlies, South Korea surrendered decisive goals near the end of the match. Northern Ireland got their second goal in the 85th minute, while Poland collected the winner in second-half stoppage time.

Shin acknowledged that his side needs to upgrade defense, and it will improve before going to Russia.

"Surrendering goals at the last minute must be fixed," he said. "We lacked concentration at the end of the match, but I think if we keep practicing our defensive plans after we gather the players in May, we'll see some improvements."

Against Poland, Shin started with a 3-4-3 formation but switched to 4-4-2 before half time. Shin defended his tactical choice, saying the back-three system is still a good option for the national team.

"We need to have a plan B," he said. "We only practiced the back-three system for a day, and because of Kim Min-jae's injury, our backline wasn't good in the match. But I don't think our plan B isn't good."

Shin said through the two friendlies, he also learned a few things on using attacking ace Son Heung-min. The Tottenham Hotspur man played left winger against Northern Ireland and started as center forward against Poland.

"Through these tests, we have to check who should be Son's partner and how he performs under certain formations," he said. "We found the formation that will best work for our team, so it was helpful."

Before the friendlies, Shin said his World Cup squad is about 80 percent completed. The 48-year-old coach said he still hasn't decided on the remaining 20 percent.

"I have to fill in the remaining 20 percent by reviewing our performance," he said. "In order to minimize risks at the World Cup, we have to make our final roster carefully."

Shin said he is still undecided whether he should further check Europe-based players like Suk Hyun-jun of Troyes and Lee Chung-yong of Crystal Palace or other domestic K League-based players who weren't called up for the friendly matches.

"I don't think I have to fly to Europe again," he said. "It's still 50-50. I'm still thinking whether I should check Europe-based players or other players in the K League."

The March friendlies were South Korea's last tests before they unveil the roster for the 2018 FIFA World Cup. Shin is expected to announce his 23-man World Cup squad in late May, though the deadline for the submission of the final list of 23 players is due on June 4.

South Korea are in Group F at the 2018 World Cup, with Germany, Mexico and Sweden.(Yonhap)