Soriano struggled at the plate and in left field last year and his struggles have overflowed into this year. Soriano is a liability defensively, and his only value is at the plate and he isn't producing there either. Soriano is hitting .200/.200/.360 through seven games so far this year after hitting .241/.303/.423 last year.
His defense has been horrible so far this year, and he was very bad in left-field last year. If his plate performance, and defense doesn't improve quickly, Tyler Colvin and Xavier Nady will likely start getting a lot more playing time. Soriano might turn into a very expensive platoon player or bench bat.
Xavier Nady is a proven hitter and a better fielder than Alfonso Soriano, but after his second Tommy-John surgery his throwing arm isn't at full strength yet. He will make all the routine plays in left-field though, something Soriano has struggled to do so far.
Tyler Colvin is a proven defender, has good speed and can play all three outfield positions. He had a spectacular spring training this year, but hasn't had much of a chance so far to show he can hit at the major league level.