Boss Michael Laudrup has been searching for another striker to boost the Swans up front after claiming just one win from their first three matches of the season in Sunday's 2-0 victory over West Brom, and the 22-year-old Spain Under-21 international would be a valued addition at the Liberty Stadium.
Laudrup has made enquiries about a number of forwards during the transfer window and confirmed Vazquez was one of the names on his wanted list last week.
And a club spokesman confirmed: "The deal for Vazquez has been agreed in principle. It's a loan deal with a view to a permanent move."
The former Espanyol youth player, who has played 89 top-flight matches in La Liga with 14 goals, helped his country to win the Under-21 European Championship earlier this year with a goal in Spain's group-stage victory over Holland.
Vazquez was keen to move on after a difficult spell with Getafe following his move last summer.
Chairman Huw Jenkins is delighted with the acquisition of Vazquez and believes he is the right man to help lead the Swans' attack.
He told the Evening Post: "Michael knows the player very well and, when you weigh up what else we have in the squad, a young player with potential who has already done well out in Spain looks like the right signing for us at this stage."
Despite being linked with Peter Odemwingie - reported to be in talks with Cardiff - and Bolton's David Ngog, it seems unlikely Swansea will add any more new signings to their squad before the transfer window closes.
Following the news on Vazquez, a club spokesman said: "That would be it for the time being."