The 22-year-old, who finised the season as the club's top striker, was offered a new deal at the beginning of the month but he has yet to put pen to paper and is rumoured to be considering several offers from other clubs.
"I have left it in the hands of my agent," May told the club's official website. "If he tells me to sign, I will sign.
"I have come through the ranks at Millwall, and you always want to do well in that situation. I was so happy to get a chance this season, and I would like to do well for this club."