As he probably should be. But Guthrie's a solid starting pitcher, much better than his 3-13 record this season suggests. Guthrie's durable, and his 4.12 ERA over the last five seasons is better than American League-average. If Guthrie were to join the Tigers, he would immediately become their third-best starter, behind only Justin Verlander and (arguably) Max Scherzer.
The club has to be careful, though. Supposedly one trade target for potential trading partners is Charlie Furbush ... but Furbush might be nearly as good as Guthrie right now. And when you calculate Furbush's value over the next six seasons -- during which he'll be under team control -- vs. Guthrie's over the time when he's under team control -- the rest of this season, plus next season -- it might be hard to argue for a deal like that.
Of course, just based on future value it's always tough to justify a deal like that.