He looks very thin and seems to have a mild case of pop eye. Is this the case or is it just the picture? The ten gallon would be fine for awhile, and may help him eat without competition, if it were established. Moving this guy into a tank that you just set up is likely to do him in. Even if you monitor the tank every day, and do water change as needed for ammonia, the tank is unstable. There will be parameter fluctuations which will add considerable stress to this guy.