Brandon League was drafted by the Toronto Blue Jays in 2001, and has made 168 appearances for the club. (Mike Carlson/Associated Press)

The Toronto Blue Jays have worked out a tentative deal that would see reliever Brandon League and a prospect head to the Seattle Mariners for pitcher Brandon Morrow.

The deal is contingent on both players passing a physical and the approval of Major League Baseball.

League was 3-6 in 67 appearances with a 4.58 earned-run average last season, with his ERA suffering a drop-off from a 2.18 showing the previous season.

The 26-year-old had an inconsistent 2009 campaign. He had several rocky outings in June and August, but started and finished the season with a string of decent performances.

For his career, he is 7-10 in 168 games with a 4.09 ERA.

"It was definitely surprising," League said. "I didn't see it coming, I was talking with my agent, he didn't see it coming.

"I guess it was a really quick thing that came up. The thing I'm going to miss are all the friends I came up with through the system over the past few years."

Morrow is a year younger than League and also a right-hander. He has displayed more versatility in his career than League, but also more volatility.

He was selected fifth overall in the 2006 draft by Seattle and has worked as a middle reliever, closer and starter in three seasons.

Morrow is 15-8 with 16 saves in 131 games, with a 3.96 ERA. He is coming off by far his toughest season, experiencing forearm tightness and a stint in Triple-A.

While League has needed to rely on his fielders to make plays, Morrow's challenge has been harnessing a lively arm. He has struck out 204 batters in just over 197 career innings, but has also walked 128.

The Mariners used him as a starter last season after he came back from Triple-A, and he finished the season with a one-hit performance over eight innings on Sept. 30 against Oakland, striking out nine and walking two.

The Santa Rosa, Calif., native was previously linked to a rumoured deal with Detroit that never materialized.

MLB.com reported that the prospect will likely be Johermyn Chavez. The 20-year-old Venezuelan outfielder hit 21 home runs in Class-A ball the past season.