After beating Cambodia 3-1 on Monday, Singapore have to defeat Indonesia on Thursday if they want to reach the semi-finals.
Sarach believes that facing Singapore will provide an accurate assessment of his side's quality and also test out whether they can handle the pressure of playing in their opponent's backyard.
"I prefer to face off against Singapore even though they have the home crowd behind them because that will test the quality of Thailand," he told reporters.
With Thailand having won all their games thus far, which included a 6-0 thrashing of Laos on May 29 and a 5-0 battering of Brunei on Saturday, Sarach is confident that his side can keep their unbeaten streak alive when they face Vietnam in their final group match on Wednesday.
"There is no extra pressure on the team because we've been together for more than a year now," he said. "This may be my first time as captain but I don't feel any pressure. We just have to play our own game."