The Magpies were close to qualifying for the Champions League last season, finishing fifth in the Premier League, and Lee said that trying to replicate this will be a difficult challenge.
"No-one expected Newcastle to do what they did last season," Lee told BBC Sport. "I was certainly pleasantly surprised, but I am sure an awful lot of Geordies were too.
"They played some fantastic football, scored some great goals and were still in the hunt for a Champions League place with two matches to go, which was incredible.
"The challenge this season is going to be how you repeat that, build on it. It won't be easy and they are facing a whole different set of challenges this season."
Newcastle qualified for Europe for the first time since 2004 by reaching the Europa League playoff stage.