Harrison is the most familiar player to Leeds fans, after he spent the season on loan with Marcelo Bielsa’s side last term.
Harrison did a solid job during his time at Leeds, after signing from Manchester City.
Frey and Hefti are the more unknown prospects for Leeds fans.
Grey is a Turkish forward who plays up-front for Fenerbache.
The 24-year-old is a powerful target-man, who hit five goals in 25 appearances last term.
Hefti, meanwhile, plays in central defence for St. Gallen.
Hefti is only 21, but he has featured regularly for the Swiss side, who rate him highly.
Leeds moving for the trio is likely to depend on Marcelo Bielsa’s future, with the Whites still working on a deal to tie down the Argentine boss for next season.
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