Blues coach Dai Young said: "It's a shame for Jonah because he was really looking in good nick and was looking forward to the rest of the season. Thankfully the injury is not as bad as we thought and the good news is that he hasn't broken anything.
"However ankle injuries are not the kind of thing you get over in a couple of days and it was badly swollen after the game and he looks extremely doubtful for Wednesday."
Team-mate Andy Powell's season is over after he broke his thumb earlier in the game. The in-form No.8 has been ruled out for six weeks and is now a doubt for Wales's summer tour to Argentina.
Young said: "Andy's injury is more serious and his season is probably over."