Toyota has described the Rebellion and SMP privateer teams as "very serious competitors" after their performances in Sunday's official pre-race test ahead of the Le Mans 24 Hours.
The Japanese manufacturer admitted to being impressed by the speed of the Rebellion-Gibson R-13 and SMP Racing's BR Engineering-AER BR1 over the course of the test day on the full 8.47-mile Le Mans circuit.
The fastest Rebellion time of 3m19.680s set by Mathias Beche was only six tenths away from the 3m19.066s Fernando Alonso posted to top the classification aboard his Toyota TS050 HYBRID and just ahead of the second Toyota in third place.
Vitaly Petrov was 2.5 seconds off the pace in the best of the pair of non-hybrid P1 entries fielded by SMP on 3m21.603s.
Toyota Motorsport GmbH technical director Pascal Vasselon said: "They are coming strongly, so we cannot rest so much.
"What we are interested in is the progress, because obviously our new competitors are not stabilised in their performance development.
"We have seen very large progress for the Rebellion and even more for the SMP cars."
Asked if he thought Toyota would have a fight on its hands in the blue-riband World Endurance Championship round on June 16/17, Vasselon replied: "It looks like that. We are already pushing and we will try to find some extra tenths."
Rebellion was content with its performance, suggesting the times from its ORECA-built contender were as its simulations predicted.
Bart Hayden, team principal of the Anglo-Swiss team, said: "We were where we expected to be, but I'm not sure Toyota was where we expected it to be.
"I wouldn't say we are hopeful of being able to race the Toyotas, but we are encouraged."
He pointed out that the privateers were also fighting against the additional lap the Toyotas will be able to do each stint and the five seconds they will gain during refuelling.
The SMP team said its focus on Sunday had been on understanding the aerodynamic revisions introduced for the test and getting its three Le Mans rookies, including Jenson Button, the 10 laps necessary to qualify them to take part in race week.
The six-tenth margin between the Toyota and the best of the P1 privateers was in line with an advantage of half a second a lap that the rule makers have set out to give the Japanese cars under the Equivalence of Technology rules used to balance the hybrid and non-hybrid P1 cars.
Toyota ended up slower than at the test 12 months ago because it did not undertake qualifying simulations with either car this time.
But Vasselon said that improvements to the TS050 since last year and high-grip levels yesterday meant that Toyota's simulations predicted that a 3m17s lap would have been possible.
That compares with a 2017 test best of 3m18.132s set by Kamui Kobayashi. Vasselon said that in terms of race pace the TS050s "were significantly faster than last year".