Phil Hughes' 2011 debut on April 3 didn't go very well. He lasted just four innings, gave up five runs, and allowed more walks and home runs (two each) than he had strikeouts (just one). Perhaps more of a concern than the poor performance was the greatly reduced velocity he showed, as his fastball averaged just 89.1 mph, significantly down from the 92.6 mph mark he displayed last year.
After watching Javier Vazquez's velocity disappear last season, the Yankees are acutely aware of what can happen to a power pitcher who suddenly loses his ability to throw his fastball with authority. However, history suggests that this isn't something to be overly concerned about yet.