The Seagulls were not even listed as candidates to sign the Owls' talisman when Sky Bet re-opened the market earlier this week, but are now 4/7 to secure his signature with no other club shorter than 18/1.
Forestieri has failed to feature in either of Wednesday's last two Championship fixtures, following an alleged bust-up with teammate Sam Winnall, for which the Argentina-born player has since apologised.
But his future at Hillsborough remains uncertain, and the Owls could look to cash in with financial fair play hindering their search for new signings.
With Sam Baldock currently sidelined, Brighton would likely have room for Forestieri, who has recently expressed a desire to play through the middle.
The 2015 signing from Watford has scored or assisted 41 goals in 78 games for Wednesday, and finished as top scorer in each of his two campaigns at Hillsborough.