Melbourne have lost forward Christian Welch in the first half of their preliminary final against Penrith after he failed a head injury assessment.

Welch was assessed on the field with commentators employing Melbourne Storm staff to get him off the ground for treatment.

Michael Ennis was direct in his opinion of the stop in play.

“You can’t stop the play and the player is allowed to remain on the field," Ennis said.

"If play is stopped it has to be so significant the player has to leave the field.

“You can hear Sutton say he has to go to the trainer.”

Gorden Tallis agreed with Ennis’ thoughts. “He has to leave the field," claimed Tallis.

“That’s what the rules should be if you stop the game at the moment, Welch has to leave the field.”

The injury wasn't the only blow to the Storm with star hooker Brandon Smith also being ruled out.

Smith appeared to hurt his shoulder in an attempted tackle where he lead with his right shoulder.

Smith's absence is a massive blow for the Storm as they look to turn the game around in the second half.