The Championship side Plymouth Argyle had a bid rejected last month, with the Skelmersdale chairman Frank Hughes saying at the time the offer was "not a million miles away from what we believe to be his true worth".
Tommy Lawson, the Skem manager, said at the weekend he hoped Donnelly's future would be resolved quickly as the speculation could prove a distraction.
Two Blue Square North sides - reported to be Southport and Fleetwood Town - have also had offers turned down.
"It is threatening to become a bit of a circus, I just want the whole thing brought to a conclusion," Lawson told the Skelmersdale Advertiser.
"There is a lot of speculation going around but we just want the best deal for the club and for the lad."
Donnelly is not he first non-league forward United have tracked this season, after failing to agree terms with Gateshead for their striker Lee Novak. Novak eventually moved to Huddersfield Town.