From 2013 to 2017, the War Elephants were the undisputed kings of the region as they won two Suzuki Cups, were one of the final 12 Asian teams contending to qualify for the 2018 FIFA World Cup, as well as claiming three consecutive gold medals at the under-23 Southeast Asian Games.
But Vietnam has emerged as the top team in Southeast Asia recently by winning the 2018 AFF Suzuki Cup to go with a runners-up finish at the AFC U-23 Championship. Last year, Vietnam reached the quarterfinals the AFC Asian Cup.
Four Southeast Asia teams -- Indonesia, Malaysia, Thailand and Vietnam -- are pooled together in the Asian qualifiers for the 2022 World Cup. Vietnam sit atop the group, while second-placed Malaysia hold a one-point lead over Thailand, with the United Arab Emirates and Indonesia lagging behind.
These are clear signs that Thailand is no longer as dominant as they once were. Chappuis, who was part of the side that won the Suzuki Cup under Kiatisuk Senamuang in 2014 and 2016, however, believes it is up to them to rise to the challenge.
"This is football - we probably started to think we were the best," the 28-year-old told ESPN. "I remember the 2016 Suzuki Cup. I don't want to come across as disrespectful but the feeling was that it was kind of easy. We went into games thinking we'd win no matter what. Now, we see Vietnam is on the top, Indonesia is close, Malaysia is coming back with a new team and so is Singapore ... that's how football is."
Despite being out of the international fold for the last few years, Chappuis is trying to force his way back onto the national team's roster by performing for new club Port FC.
While the Swiss-born midfielder has a FIFA U-17 World Cup winner's medal from 2009 with Switzerland, he counts the 2014 Suzuki Cup with Thailand as the highlight of his career.
"It changed my life totally on and off the field," Chappuis said. "I feel like we also -- as a team under 'Zico' (Kiatisuk Senamuang) -- changed Thai football, especially after that win in 2014.
"It was unbelievable when we came home from Malaysia. The people were waiting from Don Mueang [Airport] all the way to Siam Paragon [in the city centre]. I have never seen anything like this and after that life changed. Everyone knew who Chappuis was."