But Juncadella tested in 2013 for Williams, and he was in the running for a bigger role this year, "but I really wanted to drive more and be the reserve," he told Spain's El Confidencial.
"I had been in the Mercedes simulator," he said, "but this did not give me options to get in the car.
"I could only do it (get a 2014 reserve role) with teams that have Mercedes engines," Juncadella revealed.
Presumably, that is because he will combine his 2014 duties in F1 with a continuing race role in the German touring car series DTM, where he drives a Mercedes.
Williams will be Mercedes-powered in 2014, but "we decided on Force India," he said, "because they were giving the best chance to get in the car and have the most track time".
"It's a super-important year," Juncadella explained, "and it's great to have this opportunity because of what can happen in the next year.
"But we must go step by step -- I don't want to raise expectations that I can go faster than Hulkenberg or anything."