Hibs had made two offers, but their Premier League rivals stepped in to agree an immediate royalty with the Ibrox squad.
McCrorie is expected this morning at Cormack Park for his medical examination.
The 22-year-old has been on Derek McInnes’ radar for several weeks.
McInnes’ hands have been tied due to the COVID-19 situation and their staff and gaming team have all agreed to take cuts.
The problem for the Dons is that McInnes must add to his squad with eight players facing bans for coronavirus lockdown violations while Andrew Considine is suspended and Curtis Main is also injured.
McCrorie is seen as a future Scotland international, capable of playing right-back, central defense and midfielder and will give the Dons side real options.
The phased transfer fee means that all fees will come from next season’s budget and also allow the Dons to pick a promising young Scotsman in the meantime.
Aberdeen signed Jonny Hayes this summer but he agreed to defer his salary, while Tommie Hoban also signed a short-term deal to provide defensive cover.
Rangers boss Gerrard, speaking after the draw with Livingston, said: “Ross is close. He has a few options on the table. “Again, we are really waiting for a decision. ”
The Swiss side of St. Gallen also acted for McCrorie, who spent last season at Portsmouth but was unwilling to commit to a deal beyond a loan, while Hibs is likely to be disappointed after having negotiated a deal with the Rangers for several days. .
Aberdeen also doubled up on Easter Road outfit when midfielder Funso Ojo signed last season.
The Dons have shown in the past with the signings of Lewis Ferguson of Hamilton and Mark Gallagher of Ross County that they are keen to recruit emerging talent to merge with their own local talent.
McInnes also likes a striker, as he doesn’t have a leader available for Thursday’s clash with St Johnstone due to injuries and COVID-19 issues.