Kindred Group shares tumbled on Wednesday after the company missed second-quarter analyst estimates by more than 40 percent, as a result of disappointments in Sweden and the Netherlands.
Shares fell 26 percent to 60.88 kronor, the lowest level in more than four years.
Swedish profit was hurt by the need to pay betting taxes now that the market is fully regulated, plus higher promotional spending to gain market share.
Meanwhile, Dutch performance suffered from the decision to remove iDEAL, the online payment system favoured by residents there, in line with regulatory demands.
The company suffered "a huge miss which relates both to poor growth and high costs during the period. A poor combination indeed," said one analyst.