The Red Bulls currently sit on top of the overall MLS standings with four regular season fixtures remaining which has them in pole position for the minor premiership.
But Petke is not getting carried away as Seattle Sounders (one point, two games in hand), Sporting Kansas City (three points behind, one game in hand) and Real Salt Lake (three points behind) are among a group of teams breathing down their necks.
"It's great that people are excited and optimistic. But having said that, just look at our next game in Seattle," he told SI.com.
"Probably 60,000 fans there and a team that's in phenomenal form right now on prime-time TV - ESPN. I mean, if we win this game, have we arrived? No.
"We're a bad four games away from not making the playoffs. No matter what, tides turn very quickly. To talk about the Supporters Shield for myself and my players is very ill-advised and very premature."
Petke, who has grown up around the New York soccer landscape, said the major goal for the club was to take out the 2013 MLS Championship.
"Of course New York fans in all sports are fickle. It's championship or bust," he added. "For all our supporters and for who they are and how long they've been here, many have been here since 1998 when I joined the team, of course they want nothing more than a championship."