Tracy will soon return to Weatherfield with the news that she is expecting Steve's baby, but her shock announcement comes just as the Rovers Return boss is growing close to estranged wife Becky (Katherine Kelly) again.
Speaking about Tracy's bombshell, Gregson told All About Soap: "At first, Steve doesn't believe it. He thinks it may be just another one of Tracy's twisted lies. It's the worst thing that could happen at the moment.
"He can't stand the sight of the woman and now he's faced with the prospect of fathering another child with her."
Discussing Becky's involvement in the storyline, he continued: "Deep down in his heart, Steve loves Becky - but he is also a great dad, so it's not really a straight choice between the two women. For him, it's more of a choice between being a father and being a husband.
"Steve knows Tracy does love him and can provide him with the family life he craves. It will be interesting for the viewers to see which way he finally decides to go."
Kate Ford, who plays Tracy, recently signed a new deal with Coronation Street which will keep her on screen until at least January 2013.
Read more news and rumours about this storyline:-
> Becky McDonald's Corrie exit revealed?
> Coronation Street character 'to be pregnant with twins'
> Coronation Street stars film pregnancy reveal scenes
> Coronation Street Tracy pregnancy is the ultimate revenge, says Kate Ford
Watch a preview of Friday night's Coronation Street double bill in the video below: