SINGAPORE - When Khairul Amri and Hariss Harun suffered anterior cruciate ligament (ACL) tears, both feared the worst for their club and international careers. But it was not the end of the road for the Lions, with Khairul recovering to fire the national team to international success, while Hariss went on to become national captain.

In 2011, Amri was 26 and playing in Indonesia for Persib Balikpapan when he stumbled into a pothole during a league match and twisted his knee, completely tearing his left ACL in the process.

The forward said: "I cried when I saw the results and it was a complete tear. I was actually offered a two-year contract and had to turn it down because I would be out for too long and it wouldn't be fair to Persiba.

"The recovery process was crazy, and there were many times I asked myself why do I want to put myself through this, and if I should just give up. But what kept me going was the desire to play again."

ACL injuries are in the spotlight now after Liverpool defender Virgil van Dijk suffered a complete tear because of Everton goalkeeper Jordan Pickford's tackle in the 2-2 draw on Oct 17. The injury could rule him out for the rest of the Premier League season, which is a big blow to the Reds' hopes of defending their title.

Amri joined the LionsXII after Persiba, and while the goals continued flowing - he scored for Singapore in the 2012 AFF Suzuki Cup semi-final and final victories - he just felt something was missing.

He said: "I started training after six months out, but I needed another six months to get back what I lost, and to get my touches back.

"Those who knew me before the injury would know that I'm a speedy player. After the injury, I felt I had just 60 per cent of my pace."

The upside was it also unlocked a different dimension to his game as he began to analyse top strikers, following their movement, and successfully evolved to remain a productive attacker who averaged about 10 goals per season.

"I managed to change my game and become more of a thinking player," said Amri. "In the past, I would just push the ball past the opponent and beat them with pace, (but after the injury) I rely more on anticipation and reading of the scenario."

Nurhafizah Sujad, the Football Association of Singapore's head physiotherapist of national teams, explained why the ACL is important to a footballer, and why an ACL tear seems to be such a common injury in the sport.

She said: "It is one of the major knee ligaments. It forms a criss-cross with the posterior cruciate ligament and it holds the knee such that it does not go too much forward, and it also prevents the knee from turning inwards too much. This gives the knee good stability whilst doing impact exercises.

"An ACL injury often involves a rapid change in direction, sudden stops, awkward landing after a jump, or direct contact to the knee. These are common occurrences in sports like football.

"It is considered a more serious injury because it requires a long period of time for recovery and it plays an important role in the stability of the knee joint."

A 2017 article in the British Journal of Sports Medicine calculated that 83 per cent of elite athletes were able to return to sport following ACL reconstructions.

Nurhafizah said: "Many do return to play high-level competitive football, provided they have done a comprehensive rehabilitation programme. But studies have also shown many would have another episode of re-injury in the same leg or opposite leg after returning to play.

"The players will have to work with their physios and fitness coaches closely to continue to do their maintenance ACL rehabilitation programmes to prevent that from happening."

Hariss, who was just 17 when he tore his right ACL after an opponent landed on his leg during a tackle in a league game, noted the importance of mental strength and discipline in the recovery process.

Currently recovering from a left knee reconstruction after slipping during training earlier this year, the 29-year-old said: "I was just a year into my football career then, and I was scared my career would be over before it started. There were too many question marks and too much information to digest.

"It was very tough as I was juggling my studies and rehab at that time and it took me nine to 10 months to come back. Rehab was a long and hard road. It is a lot tougher than team training and you really need mental strength and perseverance. I'm also thankful for my family's support and for the coaches and physios who pushed me through.

"After I recovered, I felt I lost that yard of pace. But with proper rehab, I feel it is possible to be stronger than before, and the body also learns to adapt.

"Once you step on to the pitch again, there is that phobia of getting injured again and you tend to be more careful before you regain confidence. Once you go into the first contact or challenge and come out of it unscathed, you clear a big mental hurdle and things would seem normal again."

Different extents of an ACL injury

Grade 1 - Ligament is stretched, with no torn fibres. Recovery period is usually four weeks.

Grade 2 - Partial tear of the ligament. Recovery period can take 12 to 16 weeks

Grade 3 - Complete tear, which requires surgical intervention. Recover period is at least six months.

The recovery period depends on how well one responds to rehabilitation, as well as if other structures such as bone, cartilage, and meniscus are also damaged during the impact of injury.