"This doesn't close the door," Forst said by phone late Wednesday. "Kiko is a free agent, which puts us with the other 29 teams as far as trying to sign him, but we'll definitely be talking to him about coming back."
Calero, acquired in the December 2004 trade that sent Mark Mulder to the Cardinals, was one of Oakland's most consistent and valuable relievers in his first two seasons with Oakland, but he suffered through shoulder problems and the worst statistical season of his career in 2007.
In 46 appearances, Calero, who turns 33 in January, went 1-5 with one save and a 5.75 ERA -- 2.34 runs higher than his previous high over four seasons. His opponents' batting average in 2007 was .293, up from a previous high of .231.
Had the A's tendered Calero a contract, it's likely he would have received a modest raise over his 2007 salary of $1.6 million. Forst said the team's decision was both financial and health-related, but he added that he's received good medical reports on Calero since the end of the season.
"He's been getting physical therapy back home in Puerto Rico for the past two months, and he definitely feels a lot better than he did in the last month of the season," Forst said of Calero, who was shut down for the year after making his final appearance on Aug. 25.
Asked in mid-September if he expected to be back with the A's next year, Calero sounded cautiously optimistic.
"I hope so," he said. "I like it here, I like the team, and I want to do better for them than I did this year. I don't know what they're thinking because of the shoulder, but hopefully it gets better and we can work something out."
Oakland did resolve one of its arbitration issues, agreeing to terms with lefty Lenny DiNardo on a one-year deal.
The rest of the team's arbitration-eligible players -- righties Joe Blanton, Huston Street and Chad Gaudin -- will exchange 2008 salary figures with the club and head to arbitration if a deal can't be reached before the scheduled hearings early next year.
Mychael Urban is a national writer for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.