Alan Knill, the Iron manager, held talks with the American this week as he looks to bolster his squad ahead of the start of pre-season training on July 9.
"He hasn't just got our offer on the table, there are others too. Some of those offers will be more than we have offered, but he will have to make that decision," Knill told this club's official website.
"I am hopeful that he will come to us, but we have a ceiling on the offer because we don't have the money to go any higher."
Grella was a third round pick in the 2009 Major League Soccer draft, but instead of joining Toronto FC moved to England for a trial with Leeds United.
That won him a contract starting in February 2009. He was largely used as a substitute at the Yorkshire club, scoring five goals in all competitions.
He had loan spells at Carlisle and Swindon, before joining Brentford at the start of last season then moving to Bury in February. He made 10 appearances for the Shakers, scoring four times.
Knill has held brief talks with the agent of defender Nathan Clarke, who left Huddersfield in the summer, but no offer has been made.
Discussions with Watford over the future of David Mirfin were also brief, with the Hornets insisting he is part of their first-team plans for next season despite loaning him back to the Iron last term when he fell out of the picture at Vicarage Road.