In February, Shields inked the largest deal in franchise history at $75 million for four seasons. He's still owed $63 million on that deal.
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Shields made $10 million this past season and is set to earn $21 million in each of the next three seasons. There's a club option for 2019 for $16 million, with a $2 million buyout.
It's worth noting that Shields also has an opt-out clause after '16, should he choose it.
Shields, who will turn 34 on Dec. 20, was 13-7 with a 3.91 ERA in 33 starts in his first season with San Diego, surpassing the 200-inning plateau for the ninth consecutive season.
It was the highest ERA Shields has had since posting a 5.18 mark in 2010 with the Rays. He also allowed 33 home runs -- also his most since '10 -- and issued a career-high 81 walks.
In Shields' final start of the season, on Sept. 27 against the D-backs, he allowed four runs on nine hits, including three home runs, in 6 1/3 innings.
"That's kind of the way my season has gone," Shields said afterwards. "I've definitely thrown better, no doubt about it. … I go out there every five days and pitch with my heart on my sleeve. I'm going to be a bulldog out there as much as I can. I'm hoping for better things next year."
Moving Shields in a deal would obviously create an opening in the rotation. The Padres don't have internal candidates waiting in the wings to fill that spot.
On Wednesday, San Diego acquired left-hander Drew Pomeranz from Oakland, though general manager A.J. Preller said no decision has been made on whether the southpaw would pitch in relief or be a candidate for the starting rotation.
The Padres have also lost Ian Kennedy to free agency. The team extended him a qualifying offer, and he rejected it.
As it stands today, San Diego has Tyson Ross, Andrew Cashner and Shields as the top three pitchers in the rotation. Preller said that the Padres, among their other needs, are still pursuing a starting pitcher.