The Cubs have not commented on the reports.
Hammel signed a one-year, $6 million contract with the Cubs last February, and he went 8-5 in 17 starts before he was traded, along with Jeff Samardzija, to the Athletics on July 4.
While with the Cubs, Hammel struck out 104 batters over 108 2/3 innings, and teams hit just .222 against him, compared to .284 the year before when he was with the Orioles. Among his wins with the Cubs was a victory over the Yankees and Masahiro Tanaka at Wrigley Field, ending the Japanese pitcher's streak of 42 unbeaten regular-season starts.
The Cubs had pursued Tanaka as well, but lost in that bidding. Hammel was well aware he was Plan B.
"It just kind of goes to show that sometimes you don't have to go out and spend all the money to get that superstar player," Cubs catcher John Baker said last July after the win over the Yankees. "Sometimes that guy is just kind of lying in wait."
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.