Michael Bowden is the player Rosenthal is referring to. He was ranked somewhere in the 10-12 range of the Red Sox top prospects in 2010. The 25 year old has pitched three innings for the Sox this season. He struck out three batters wile allowing one run.
He's pitched a total of 59.1 innings in the bigs and owns a 5.61 career ERA. His fastball sits in the lower 90s and is fairly below average at inducing swinging strikes.
Byrd still has some value, especially if the Cubs are willing to pay the bulk of his contract.