The box-to-box midfielder has looked sharp in Wednesday's opening two league fixtures, having put an injury-plagued 18 months behind him.
Lee, who moved to Hillsborough on a free transfer in the summer of 2012, has acquitted himself well in the Owls' three-man midfield and was given a standing ovation when subbed off in the 80th minute of Saturday's 2-0 win over Barnsley.
Bullen, in his third spell as caretaker manager of the Owls, said: "He is a talented, talented footballer. Even through injury, we knew his class was still there.
"Even around the 30-year-old age, he has probably covered more miles than anybody else on the football pitch.
"He is just one of these players that you don't notice for 65 to 70 minutes and then you suddenly realise he is clearing it off the line in one box and getting on the end of something in the opposition's box."
Lee, a key man in the Wednesday team that reached back-to-back play-offs under Carlos Carvalhal, has struggled to stay out of the treatment room in recent years.
But Bullen is determined to closely monitor Lee's fitness.
"Listen, he is a coach's dream but we have to manage him right," said Bullen, who has presided over Wednesday's best start to a league season in 23 years. "We have to be careful.
"We have to remember he has been out a long time and he is not going to play every game.
"Luckily enough our transfer window went very well and we have strength in depth for a lot of positions and that quality now in the midfield area, even without Barry Bannan."