Zapata is less clear cut, what with the major injury problems he's had in his career.
People use that 'injury prone' and 'big injury' way too often when it comes to Zapata.
Only in the season 08/09 he played like 10 matches less than he's supposed to, due to his injury. His other injury only infected the summer period.
In last two seasons he played 35 matches in Serie A (Chiellini had 32).
That being said, Zapata for ~8mln was a steal, as he's a great player.