Son Heung-Min, Ki Sung-Yueng under World Cup cloud for South Korea

These are troubled times for South Korea. Son Heung-Min and Ki Sung-Yueng are not only in danger of missing the start of the new Premier League season, but could be absent, or short of fitness, for do-or-die 2018 AFC World Cup qualifiers against Iran and Uzbekistan, starting next month.

June's loss to Qatar was seismic for a number of reasons. For one, it resulted in Son breaking his arm. The forward had a fine season for Tottenham Hotspur, scoring 21 goals in all competitions.

Few Asians have had such explosive European campaigns, but the next one may have to wait. The London club said that the soon to be 25-year-old would be "monitored by our medical staff ahead of a return to action next season."

Son is not expected to head to the U.S. later this month for preseason games with Paris Saint-Germain, Roma and Manchester City. He may also miss for the final warm-up match against Juventus at Wembley on Aug. 5, a week before the season kicks off at newly promoted Newcastle United.

A similar statement came out of Swansea City as Ki Sung-Yeung also left South Korea's qualifier in Doha, and headed to the operating theatre to sort out his knee.

Swansea City announced last week that the 28-year-old will miss their trip to the U.S. where they will play the likes of Philadelphia Union and Richmond Kickers before lining up against Spurs on the opening day of the Premier League season.

"He will remain in South Korea to continue his rehabilitation, before returning to Swansea after Paul Clement's squad return from their pr-season tour to America," the club said.

It could be that Swans' fans will not be quite as upset as those in North London.

Ki's high point in South Wales came in a fine 2014-15 season when he scored eight goals. Subsequent injuries have not helped, but he has yet to match such form since. With 12 months left on his contract, it would be no surprise if one of Asia's classiest midfielders headed for pastures new.

While their absence can be problematic for clubs, it is South Korea who may suffer most as World Cup qualification enters its climax. Even if Ki and Son recover in time for mid-August when the next squad will be named, there will be questions over match fitness and form.

The Taeguk Warriors are having a hard enough time trying to qualify for the 2018 World Cup as it is. It is only due to the failings of others that South Korea are still second in Group A, despite losing three of their last five qualifiers.

Only the top two go through automatically to Russia 2018. Iran, seven points clear at the top, took the first Russian spot with a game to spare. That leaves Korea and Uzbekistan -- with Syria still having an outside chance -- scrapping for the second.

The Koreans have two games remaining. The first is at home to Iran on Aug. 31 and then in Uzbekistan five days later. Whatever happens, a win in Tashkent will do the job.

But that is not going to be easy for a team who have collected just one point in four away games so far, and failed to score in three. If the second qualification spot goes down to the final game, then the Uzbekistan trip is not going to be a place for the faint-hearted, something that Korea have been a little too often in recent times.

Son's performances for his country have always been mixed, though that is not always his fault. The Spurs' star tends to try and do too much for the national team, and sometimes cuts a frustrated figure. Despite that, he can make things happen.

Ki would be just as big a loss, even bigger. The captain has not been at his best along the road to Russia, but has suffered from the defensive fragility and tactical rigidity around him. Approaching the century mark of international caps, Ki's experience and composure will never be more vital for his country than in the next few weeks.

The games are huge, and that is reflected in the fact that the 2002 World Cup semifinalists have a new coach, with another consequence of the Qatar defeat being the dismissal of Uli Stielike. The result erased any confidence at the Korea FA that the German, appointed in 2014, could secure that Russian spot.

Shin Tae-yong is the new man. The 46-year-old is a former assistant to Stielike, but better known for leading Seongnam Ilhwa Chunma to the 2010 AFC Champions League title. More recently, he took the Under-23 team to the quarterfinals of the 2016 Rio Olympics, and then the younger side to the second round of the U20 World Cup earlier this year. Both performances were adequate, without quite being what was wanted.

Yet Shin likes to play attacking and aggressive football. If he can find the right roles for Ki, and especially Son, then South Korea have what it takes to get to Russia, without having to bother with playoffs. That is, if they are available and fit.