Boston Red Sox co-owner Tom Werner said the franchise has had discussions with Chris Sale about a contract extension before he hits the open market following the 2019 season.

"We have had private conversations," Werner told WEEI's Mut and Callahan. "The best thing for us is to keep these conversations private because he and we have to come to an understanding that is good for both sides. In a perfect world, we'd love to have him back. He's one of the great pitchers in the American League."

Sale, 29, will make $15 million in the final year of his contract. He has spent the last two seasons in Boston and recorded the final out in the team's 2018 World Series championship.

Werner said the Red Sox have also had discussions with Mookie Betts, who is playing under a $20 million deal in 2019. He will have one more year of arbitration before he can become a free agent in 2021.

Boston has not discussed a contract extension with J.D. Martinez, who can opt out of his deal following the 2019 campaign.

Martinez signed a five-year, $110 million contract with the Red Sox before last season. If he repeats his 2018 performance, it would be a surprise if Martinez did not opt out in search of a longer-term deal. Martinez hit .330/.402/.629 with 43 home runs and 130 runs batted in, finishing fourth in the AL MVP voting. 

The Red Sox got Martinez at a relatively low cost because of his injury history. The 2018 season was just the second time in his career he did not miss 30-plus games.

Sale also has injury questions after a shoulder injury plagued him for much of the second half. He did not require surgery and is expected to be 100 percent in 2019. 

Werner acknowledged that any potential long-term deal with Betts would have to wait until Bryce Harper and Manny Machado set the market for superstar free agents. Harper and Machado remain unsigned with spring training underway.