I don't agree entirely (with Jim).
Derek Fisher's floor is worse than a 4th OF. For a fast and toolsy OF prospect he has not been a particularly good baserunner in his MLB career and he has only been a +5 OF per 150 games while playing mostly LF. Compare that to someone like Jake Marisnick, who does have a legit 4th OF floor, and Fisher is starting from a big deficit.
I think he either hits enough to be a starter or a platoon outfielder, or he might not be a major leaguer.
Of course the defense and/or baserunning could improve... but I think he'll live or die on the patience and power as carrying tools. I think his most likely outcome is a replacement level, zero WAR career.