What started as trading R.A. Dickey for multiple prospects had become potentially something bigger yesterday.

As first reported by The Post, the Mets were close to a seven-player deal with the Blue Jays, according to sources, that would send the NL Cy Young Award winner to Toronto for stud catching prospect Travis d'Arnaud. In addition, the Mets would send catcher Josh Thole and a non-elite prospect to the Blue Jays for their top pitching prospect, Noah Syndergaard, catcher John Buck and another non-elite prospect.

Not a possibility for the Mets, according to an industry source, was receiving highly regarded outfielder Anthony Gose.

The remaining hurdle yesterday, according to sources, was the Blue Jays receiving assurance Dickey, who will make $5 million next season in the final year of his contract, would sign a two-year extension.

The 23-year-old d'Arnaud remains the key to the deal for the Mets. He is regarded as the top catching prospect in baseball and the best overall hitter in the Blue Jays' farm system.

In 67 games at Triple-A Las Vegas last season, d'Arnaud hit .333 with 16 homers and 52 RBIs before a knee injury ended his season in late June.

"He's a solid defensive catcher with some power," an NL talent evaluator said. "You can throw those Vegas numbers completely out of the book [because of the altitude]. But he's going to be an upgrade for sure."