MacNulty, a Republic of Ireland U21 international, came through the youth system at Betis before leaving for VfL Wolfsburg.
Along with Betis, Leeds, Southampton and Leicester are also watching the youngster.
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My dream was to be a footballer and play at the highest level. I don't care that for that I have to spend several years away from home," Garca MacNulty said, before being asked about an eventual return to Benito Villamarn.
"Of course it is a dream to play for Betis, but now I focus on what I do with Zwolle."