Korea on Monday unveiled their 20-man squad for upcoming friendly matches against Spain and the Czech Republic, as some players who have been struggling with their European clubs were left out.

Korea, 54th in FIFA world rankings, will take on No. 6 Spain on June 1 in Salzburg, Austria, and face the No. 29 Czech Republic on June 5 in Prague. They will be Korea's first matches against European nations since Uli Stielike became head coach in September 2014. They're also designed to help Korea prepare for the final Asian World Cup qualifying tournament starting in September.

"We have been expecting matches like this," Stielike said at National Football Training Center in Paju, north of Seoul. "We now know our level in Asia, but this is a good opportunity to find out where we belong on the world stage."

For the friendly matches, Stielike said he only selected 20 players because he didn't want to waste any players sitting on the bench.

"We have been taking 23 players for these kinds of matches, but four or five players have always been on the bench, including the team's third goalkeeper," he said. "The players will have to take a long trip to Europe, and I want every player to feature in the matches."

Those who've failed to feature regularly with their European clubs this season were left out, including Lee Chung-yong of Crystal Palace, Park Joo-ho of Borussia Dortumund and Kim Jin-su of Hoffenheim.

However, other Europe-based players such as Ki Sung-yueng of Swansea City, Son Heung-min of the Tottenham Hotspur, Suk Hyun-jun of FC Porto and Ji Dong-won of FC Augsburg made the list.

Lee had a troubled season in the English Premier League (EPL) both on and off the pitch. The 27-year-old played only 385 minutes in 13 matches at the Palace and was recently fined by the London club after criticizing manager Alan Pardew in an interview with South Korean media.

Kim ended up playing only 15 matches this season in the German Bundesliga and had not played in league matches since Feb. 1 against Bayern Munich.

Park completed the season with five Bundesliga matches and four UEFA Europa League matches under his belt. His last league appearance with Dortmund was on Jan. 23 against Borussia Monchengladbach.

"They didn't play regularly with their clubs and, on some occasions, they were not even included in the match squad," Stielike said. "In the previous call-up, I said that it will be difficult for me to select such players again if their situations didn't improve, and it turns out their situations didn't change."

Stielike said that the void left by Kim and Park, both left backs, will be filled by free agent Yun Suk-young and Al-Wahda back Rim Chang-woo. Yun, who played with Charlton Athletic this past season on loan from the Queens Park Rangers, made the national team for the first time in 14 months.

Stielike said he chose midfielder Yoon Bitgaram to fill in for injured veteran Koo Ja-cheol in the midfield. Yoon, who plays with Yanbian Funde in the Chinese Super League, has returned to the Taeguk Warriors for the first time since September 2012.

Stielike said he will also try Sangju Sangmu's Lee Yong at right fullback since he could be "a great replacement" for injured Kim Chang-soo. (Yonhap)