Morrison, who recently said that he wants to direct the show, told Zap2It that it has been "so great" working with Gwyneth Paltrow.
"Just having an Oscar-winner in your midst, everyone brings their A-game to set," he said. "It raises the bar of expectations.
"But I think that [Holly's] kind of a flighty character, so I think that [romance is] only going to last as long as she can have it last."
However, Morrison hinted that Will and Emma (Jayma Mays) could start to have more scenes together.
"I don't know what's going to happen but I think [Emma and her husband Carl] are going to have a little rocky relationship coming up," he teased. "And I think towards the end of the season they're really going to pump up the Wemma storyline... I'm looking forward to that, a lot."
Glee returns for a new episode in the US next month and continues in the UK on Mondays at 9pm on E4.
> 'Glee' star expects Will, Emma romance