Red Bull Salzburg have made clear to Leeds that they do not want to sell the American during this month’s transfer window due to their continued involvement in the Champions League.
Leeds have already seen an offer of £15m rejected by the Austrian giants, but it has only served to increase their efforts.
A travelling party, including director of football Victor Orta, have headed to Austria for talks.
It was suggested Leeds would increase their offer for Aaronson by a further £5m.
And the Premier League side have now done so, putting in a formal bid of £20m to take the attacker to Elland Road during this month’s window.
Leeds will wait to see if increasing their offer by £5m is enough to do the trick or at least push Red Bull Salzburg to negotiate.
The Yorkshire giants have made Aaronson their priority target during this month’s transfer window and are determined to push hard to sign him.