But Naitanui has been kept out of the first two pre-season matches due to back tightness and is touch and go to play in the Eagles' next NAB Challenge clash against Port Adelaide on Sunday.
Sinclair was vying with Lycett for a spot as the No.2 ruckman and looked in contention following two strong performances.
Lycett will now shoulder the load in the pre-season given Sinclair's injury and the doubts over Naitanui.
The Eagles have trained Fraser McInnes, a 197cm forward/ruckman, to fill a ruck post if necessary.
McInnes was recruited with pick No.28 in the 2011 NAB AFL Draft but has yet to play an AFL game. He has played six pre-season matches across four seasons.
Promising swingman Jeremy McGovern can also play in the ruck but his services will be needed in both defence and attack given the season-ending injury to Mackenzie and the likely unavailability of forward Jack Darling in the early part of the season.