ASEAN markets have been among the top performers in the past two years, with Indonesia and the Philippines two of the standouts.
The Philippines was named one of the world's five hottest stock markets by business website CNNMoney in April and was upgraded to investment grade by international credit rating agency Standard & Poor's (S&P) and global rating agency Fitch Ratings.
This means that more foreign investors will be attracted to the country, since most foreign funds are only allowed to hold investment-grade assets rated by either S&P or Moody's Investors Service.
While the Filipino rally might encourage some to enter the market, Mr Alan Tan, senior ASEAN equities fund manager at Lion Global Investors, says that shares have already run up significantly.
"I'm underweight because the valuation is very high. On an average basis, this year the price-to-earnings (PE) ratio is 21 times, the highest in the region, excluding Japan," he says.
The PE ratio is a standard measure showing how the market values a particular share in relation to the firm's earnings.
A high average PE, as in the case of the Philippines bourse, indicates that investors see the shares as overpriced. It can also mean markets have high expectation of growth in the stock.
Mr Tan, 44, manages a number of funds, including the LionGlobal South East Asia Fund, the LionGlobal Singapore/Malaysia Fund and the LionGlobal Malaysia Fund.