Lee was forced to limp off after just six minutes of Tuesday's 1-0 win over Southend. The midfielder was duly replaced by Dack, who went on to win the Gills' decisive penalty before seeing red on the stroke of half-time for a nasty foul on Mark Phillips.
Dack now serves a three-match suspension, starting this weekend against a Vale side who, like Gillingham, have won their last three matches and know victory will see them leap above the Kent outfit into top spot.
Striker Weston and midfielder Payne both missed out altogether against Southend having failed late fitness tests and the pair will again be missing at Vale Park.
Manager Martin Allen has also revealed another couple of unnamed players are nursing knocks ahead of the encounter and stressed his side, despite their impressive form, needs freshening up.
Gillingham have also signed Nottingham Forest striker Robbie Findley on a one-month loan deal and he goes straight into the side.
Doug Loft has declared himself fit to play so Port Vale manager Micky Adams is likely to name an unchanged starting XI for the ninth successive match.
Skipper Loft required stitches in a shin injury during the impressive 5-2 victory at Fleetwood on Tuesday night but the midfielder is not a concern ahead of the visit of the League Two leaders.
Ahead of the game, Adams, whose side are the leading scorers in the country with 21 goals in seven league matches, said: "They're top of the table and a confident unit who've got good players and a system that suits the.
"The manager will force them forward and they look a decent side who are a real threat to us. But if we beat them we go top, so it's all to play for."
The Vale boss revealed at his pre-match press conference that there may be divided loyalties in the Adams family on Saturday as his daughter still lives in Gillingham and is a season ticket holder at the Kent club.