Aberdeen will not be able to secure transfer target Stevie May until after the Europa League transfer deadline has passed.
Pittodrie boss McInnes wants the Preston North End striker to bolster his attack in the bid to reach the lucrative group stages.
The Dons have yet to make a formal approach to Preston for May but are preparing a £250,000 bid.
However, Preston boss Simon Grayson will not make any decisions on whether to retain May or make him available for transfer until he has watched the striker in a number of pre-season friendlies.
Preston’s first friendly is on July 7 with further games on July 15 and 18.
The UEFA deadline for teams to register players for the Europa League second qualifying round, where the Dons enter, is midnight on Friday, July 7.
Any player signed after that date will be ineligible for the round’s two ties.
Aberdeen will face either Kazakhstan’s Ordabasy or Siroki Brijeg of Bosnia and Herzegovina in the second qualifying round, with the first tie on Thursday, July 13.
Should the Reds progress, any signings would have to be completed by midnight, Friday, July 21, to be eligible for the third qualifying round.
Preston have four friendlies before that deadline.
Pittodrie boss McInnes attempted to sign May from Sheffield Wednesday on loan in summer 2015 but the Scotland cap opted to move to Preston in an £800,000 deal.
McInnes again tried to secure May on loan this January and has kept in regular contact with the Deepdale club since then about the striker.
McInnes previously worked with May at St Johnstone and handed him his professional debut at 16-years-old.
Aberdeen hope to push through a move for May soon.
However, the Dons will have to sweat it out for an answer on whether May will be made available for transfer.
The striker has only recently returned from a career-threatening knee injury that ruled him out for more than a year. May ruptured three ligaments in his knee in a match against Fulham two years ago.
May defied the surgeons who said he would never play football again when he scored his first goal in over 25 months in April.
Preston boss Grayson will not make any decision until he has watched the striker in action and given him time to prove himself.
If May impresses in pre-season he could yet start the season at Deepdale.
Preston stuck by May during his rehab and he also represented a significant investment at £800,000.
Should Grayson decide to jettison May it will not be a cut price deal and Preston will hold out for £400,000.
Preston’s first friendly is against non-league Bamber Bridge on July 7 – the Uefa transfer deadline for the Europa League second round.
Should Grayson decide May has no immediate future at Preston, the Dons will likely face a battle for the Scotland cap who has a year left on his deal.
Hibs, Hearts, Dundee and a number of English Championship clubs had targeted May in January when he was still recuperating.
Now fully fit he will likely attract more attention.
Fresh reports surfaced today that Aberdeen had also renewed their interest in signing Birmingham striker Greg Stewart on loan although boss Harry Redknapp had earlier insisted Stewart’s wages would be too much for Scottish clubs.
The Dons were also linked with taking Welsh midfielder George Williams in on loan from Fulham.