Rondon was recalled to the starting XI against Crystal Palace – but he lasted just 45 minutes.
The on-loan striker was forced off with a thigh problem after an “uncomfortable” first half at Selhurst Park on Saturday.
Rondon was replaced by Joselu in the game, which ended 0-0.
“He was feeling a little bit tight,” said United manager Rafa Benitez.
Asked if his withdrawal was precautionary, Benitez added: “No, he was not feeling well. It’s not a precaution, as he couldn’t continue.
“You could see that he was uncomfortable in the first half.”
Rondon is being assessed ahead of the Leicester game.
“It’s too early (to say if he’s doubtful),” said Benitez.
“He said that he was fine. He was feeling a little bit when he was shooting.
“He said he was fine, but after you could see that he was not comfortable.”
The Palace result left Newcastle third-bottom.
“We knew before the game it could be very difficult,” said Benitez.
“The team is a team with experience, they have quality in middle of the pitch, physically they’re strong. It’s a team with experience and quality and players up front that can make a difference.
“The second half they were pushing harder and we had to defend. In our situation we have to be sure the team played as a unit and we did it.
“We were missing the final pass. A point is a point now.”