Lawson is replacing dropped Australian Daniel Ricciardo for the last six races of the season alongside Yuki Tsunoda at the Red Bull-owned RB team, with Austin a sprint weekend on October 19th-20th.
The Kiwi impressed after five races last season when Ricciardo was injured and is being assessed for a 2025 drive with RB and a possible longer-term future with Red Bull.
"In Austin, he'll be taking an engine penalty there anyway," Horner told Formula One's F1 Nation podcast. "So he's got a bit of a soft landing, or soft re-entry.
"But of course he's going to be gauged against his teammate.
"He was very quick against him last year, I think Yuki stepped it up a gear again this year so it's going to be fascinating to see how quickly he adapts, how quickly he gets on with it."
The penalty, inherited from Ricciardo, for exceeding the season's engine allocation is 10 places in the first instance.
Lawson told the New Zealand Herald that he needed to perform and nothing was set in stone.
