Sjöström gave up this weekend's competitions with his team Energy Standard.
"Unfortunately, I have had some minor back problems in recent days and I follow the medical advice to rest," the star wrote on Instagram then.
But now the Swede is giving the go-ahead for tomorrow's match against the Toronto Titans, where the Swedes Erik Persson and Louise Hansson, among others, are swimming.
- It will not be as tough a program as in my first race, then I ran nine disciplines, it will be much smaller than that.
I just want to check the situation how the back can handle the load, says Sjöström to SVT Sport.
Eight teams advance to the semifinals
The competitions in Budapest are decided in Duna Arena, the same pool that Sjöström was successful in the WC 2017 with three gold and one silver.
ISL is a mixed team competition in short course (25-meter pool) with ten teams that meet in matches and collect points.
The basic series is decided in October-November and then the eight best teams reach the semifinals.
The four best teams from there will then compete in the final later in November.