Soliola, from New Zealand, required hospital treatment after he was found by police outside Imperial Bar on Ormskirk Street at about 2.20am.
A 19-year-old man was also injured in the attack, details of which have not been disclosed.
A 32-year-old man from Speke, Liverpool, a 23-year-old man from Lymm, Cheshire, and a 24-year-old man from Chester have been arrested.
It is unknown whether the attack has left Soliola, a centre, fit enough to play against Bradford Bulls on Saturday.
The Kiwi has been a regular on the pitch for St Helens this season, including in the game lost to Hull FC on Friday.