Bentley has impressed down in League Two and is tipped to have the potential to go right to the very top of the game.
Southend, understandably, are keen to keep the stopper but, with interest growing, they may be resigned to losing him should a big offer come in.
Brentford have had a bid of £500,000 turned down in recent times, but Forest and Leeds are still keeping a close eye on the 21-year-old in the hope of securing a deal in the future.
At this moment in time neither of the clubs can arrange a deal with Southend as they are both under a transfer embargo, but he could be a signing they consider in the summer window.
Forest are on the hunt for a replacement for Karl Darlow, who will move to Newcastle United in six months' time, while Leeds current goalkeeper Marco Silvestri has had an erratic debut season in England so far.
Bentley has played 27 times for the Shrimpers so far this season and will be a key player as they chase a promotion spot between now and the end of the year should they keep him beyond the January transfer window.