The Socceroos forward has been in red-hot form in recent weeks, contributing seven goals in eight games to push City up the A-League Men ladder.
Leckie suffered an adductor injury in the draw against Perth Glory and Kisnorbo was unable to provide a timeline for his star striker's return.
The coach, however, wants others to step up and stake their claim.
"We'll have to wait for his results, but it's another opportunity for someone else to come in as well," Kisnorbo said.
"The player's welfare is the most important thing for me.
"It could be (Marco) Tillio or Stefan Colakovski, a few players could come in and it definitely gives an opportunity for our young players."
Kisnorbo is hopeful of having Aiden O'Neill back on deck, but the uncertainty over Leckie's fitness will be concerning for Australia coach Graham Arnold ahead of crunch World Cup qualifiers against Japan and Saudi Arabia later this month.
Kisnorbo said he wouldn't rush the forward back and indicated the Socceroos' games were not part of his thinking.
"I'm not the national team coach, how we can get him right for us in the safest way (is most important)," he said.
"I haven't seen the report and the time situation. I know over the past I've seen players that we have to get back as safely as possible.
"Time will tell. Who knows what will happen in that space when the Socceroos have that game in March."
Sunday's opponents Wellington come into this one without having played in the last two weeks due to postponements.
Phoenix head coach Ufuk Talay will be without Gary Hooper and Reno Piscopo as they deal with calf issues.
The City game marks the start of four games in 14 days but the Wellington boss said he would take team selection on a game-by-game basis.
"We want to play as many games as we can and finish the season in a strong spot," he said.
"I can't predict the future but if we need to utilise the players within the squad, we'll do the best we can.
"We don't have reserve grade so we'll try to fit in a friendly to get them some match minutes."
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