"I actually joked with him yesterday that he was getting traded," Haren said.
On Tuesday, Jackson was informed that he indeed had been dealt to the A's in exchange for Minor League pitcher Sam Demel. Arizona also sent a little less than $400,000 to help offset what is left of the $3.1 million owed to Jackson this year.
"I'm going to stop joking with people," said Haren, a former A's pitcher. "Anytime someone gets traded, it's surprising. Sometimes the grass is greener, sometimes it isn't, but Conor is one of my good friends, so I really hope he goes over there and enjoys it. Being in Oakland before, it's a fun place to play. I think he'll be just fine there."
Jackson, 28, was hitting .238 with 11 doubles, one homer and 11 RBIs for the D-backs after missing most of last season due to illness.
Demel, 24, was 2-0 with a 1.26 ERA and six saves in 22 games for Triple-A Sacramento. The right-hander will join the D-backs on Wednesday in Boston, at which time the club will make a corresponding roster move.
"He's a good pitcher," D-backs manager A.J. Hinch said of Demel. "He's performing very well in Triple-A and his next step is to be tested here, so I look forward to seeing him. We acquired him for a reason, and hopefully he responds to the opportunity."
Infielder Tony Abreu was activated from the 15-day disabled list to take Jackson's place on the roster. Abreu had been out since spraining his left wrist on May 25. Gerardo Parra will likely get the bulk of the playing time in left field with Jackson gone, and the team is likely to recall outfielder Cole Gillespie from Triple-A Reno once he recovers from a bout with the flu.
Demel was initially selected by the Rangers in 2004 First-Year Player Draft, but he instead elected to go to Texas Christian University and was subsequently drafted by the A's in the third round of the '07 Draft.
"We liked him out of the Draft and have followed him since," D-backs general manager Josh Byrnes said. "Obviously we feel like he's big league ready. We've always like his stuff and he's performed well through Triple-A, so we'll give him a shot."
A closer at TCU, Demel has posted a 9-8 record with a 2.79 ERA and 42 saves in 151 relief appearances during four Minor League seasons in Oakland's system. He ranked third in the A's farm system with 14 saves in 2009 and second with 18 saves in '08.
The move saves the D-backs quite a bit of money. Jackson would be eligible for salary arbitration next year and would certainly get a raise despite his struggles at the plate.
"In [this] case, it wasn't so much about financing, it was more so about improving the bullpen and getting a good young arm in here that's going to be part of this club for a while," D-backs team president and CEO Derrick Hall said.
Byrnes, though, said Jackson's potential salary for next year could not be overlooked. In fact, the D-backs would have faced a decision as to whether they could afford to offer him arbitration or would need to non-tender him.
"We aren't where we need to be in the standings, and as far as the sort of things we'd like to do to adjust the roster, there are also payroll considerations," Byrnes said. "Conor heading into his last year of arbitration was a maybe whether we could go ahead on the tender with him. It's going to be part of [the decisions], talent and cost for next year as we go."
Hinch said he was not sure yet what Demel's role would be in the bullpen, but one thing that was certain was he would not be the closer.
"He won't close anytime soon," Hinch said. "We got back a pretty good young arm that we'll take a look at and move on from there."
Jackson, who was initially drafted by the D-backs in the first round of the 2003 First-Year Player Draft, was popular inside the clubhouse as well as in the front office.
"He's a class act," Hall said. "He's done a lot for this organization, which is the toughest part of all. When you know you need to make moves, unfortunately it's going to result in having to part ways with guys like Conor who are a big part of who we are."
Steve Gilbert is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.