The £25million signing from Manchester City made his bow as Leicester defeated German side Borussia Monchengladbach 2-1.
Iheanacho came on the 66th minute and set up Jamie Vardy for the winner but was then replaced by Leonardo Ulloa after an awkward challenge.
Foxes boss Craig Shakespeare said: “I am still looking to find out. I don’t know whether it is ankle or Achilles.
“He was up on his feet, and the first thing is for me is the physios are not showing a great concern, which is a good sign.
“Vards wanted back on that scoresheet and it was very unselfish of Kelechi to lay it on a plate for him as well because someone making his debut, coming on, could have easily been a bit more selfish there.
“He’s fine in there and getting a bit of a rib from the players in terms of him coming off.
“But you can see the impact he’s had. We’re really just making sure that was more of a precaution.
“We’ve had a look at him in training. He hasn’t trained very often so far – he hasn’t been able to because of circumstances.
“But the more minutes we can get him on the pitch the more that he’ll be liable to last 90 minutes.”
