A switch to Portugal is an "important step" for the Costa Rica international striker, who has struggled to make an impression at the Emirates
The forward has been a perennial fringe player at Emirates Stadium since joining in 2011 and he was eager to prove himself somewhere at a first-team level.
"I am at an important step in my career and saw that I would not have many chances to play at Arsenal, so I asked to go on loan," the 24-year-old told Sportmasta.
"I could have chosen to stay, have a good salary, but I'd rather go after my dreams.
"I want to continue to develop and maintain this passion for the game.
"Sporting is a good opportunity in my career, a great team. I am happy with the decision I made."
The Costa Rica international was last on loan at Villarreal, having made only 23 Premier League appearances for the Gunners.