Argentinian Ulloa is leading the line for the Seagulls in the absence of the injured Craig Mackail-Smith and Will Hoskins and with Ashley Barnes serving a lengthy suspension.
His two goals in Sunday's 3-0 win over derby rivals Crystal Palace took his tally to eight in 11 matches.
But Poyet said: "I have to because it's a big risk. Imagine if we do well in the next three or four games and then something happens to Leo.
"Then I'd have to get changed into my number 45 shirt, and we cannot take that risk.
"Something will come up. Everyone is waiting until the last minute, but by a week on Thursday I will make sure we get the best player we can."
Ulloa has made a stunning impact since joining for £2million from Spanish side Almeria in January, and on Sunday outshone Palace's 30-goal former Brighton striker Glenn Murray.
"He is the kind of centre-forward we have missed for a year and a half since we lost Glenn," added Poyet. "We were looking everywhere but we couldn't find him. Can you imagine if we had had him since August?
"He has been different class. His football is perfect for England. I don't want to say too much because we might lose him. But if there is someone who deserves a two-week international break, it is him."