Then came the biggest hurdle of his career when Harris was diagnosed with testicular cancer in July 2001. Doubts were raised about whether he would play football again, but Harris beat the disease and returned to action four months later.
His form, however, suffered in the wake of the illness and, in 2004, Harris was sold to Nottingham Forest but struggled to make an impact.
After a season-long loan at Gillingham, his contract at the City Ground was terminated and Harris returned to Millwall in January 2007 to try to win over Jackett once more.
Strong performances towards the tail-end of the last campaign won him another year's contract and the chance to become Millwall's greatest goal-scorer.
Harris, who opened his account for the season with two goals in Saturday's 3-1 win against Leeds, said: "This is my club and I love playing here. Millwall is a way of life for a lot of people.
"You have to try to explain to the new lads that come in that we play a certain way for the fans to get behind us.
"If you don't put the work in they boo you, but if you play badly and work hard they give you a chance.
"My family and everyone at Millwall are desperate for me to get the record but it is one goal at a time for now."
It would be fitting if Harris, who has just returned to the side following a back injury, did break the record against Colchester for they were the last side former England striker Sheringham played for before he retired last season.
Three points would also extend Millwall's excellent start to the campaign, and Jackett said: "I came in last season and we needed to stay up. That was a big thing and now after doing that we have to go one stage further and improve on that."
