Valentino Rossi believes this week's private MotoGP test at the new Austin circuit could be his and Yamaha's 'most difficult' of the pre-season.

Denied dry track time last November, the seven time MotoGP champion began real preparations for his Yamaha return during the pair of official Sepang tests in February.

Honda then announced plans for an Austin test, from March 12-14, with the Factory Yamaha team subsequently adding the outing to its agenda. LCR Honda is also scheduled to be present but others, including the factory Ducati team, will not make the lengthy trip to Texas.

The final official test will then take place at Jerez from March 23-25.

"Austin will be very important, because in my mind I think at Sepang we are competitive," Rossi told reporters during his daily debriefs at Sepang. "I am not so bad and the M1 is always fast at Sepang. I think and I hope it will be the same story at Jerez, also a very good track for me and the M1.

"But Austin will be another story because we've never seen the track. We don't know. Maybe it will be the most difficult test, to understand our performance on what might not be a positive track for us.

"So I think it will be very important to understand the level of the bike and understand the track," he added. "It will also be very interesting to understand the level of Honda at Austin compared to us."

Rossi was third (+0.442s) at the opening Sepang test, but slipped to fifth at the return visit, when team-mate Lorenzo set the pace with a best lap 0.780s quicker than the Italian. Rossi felt circumstances had exaggerated the time difference between them.

"For me the real gap is less than 0.780s," he said. "Because Jorge worked very well and had zero problems. All the Yamaha [technical] problems were just on my bike! I was closer to Jorge until we started to struggle with our problems, so for me the real gap between us is less than half a second. But, for sure, Lorenzo is faster than me right now."

Reigning double champion Lorenzo expressed his relief that Yamaha had decided to attend the Austin test, which held its inaugural F1 event late last year and will host round two of this year's MotoGP championship.

"It's a new track so not going would have been very bad for us, they [Honda] would have had an advantage if they went and we didn't," commented the Spaniard. "Luckily finally we will go and be in the same condition as Honda for the Texas race. This is positive."

2012 title runner-up Dani Pedrosa set the pace for Honda at the first Sepang test by 0.329s over Lorenzo, before Lorenzo gained the edge by 0.280s at the second.

However, Pedrosa has so far led five of the six days of 2013 testing.

"It's difficult to say [if Pedrosa and Honda are ahead]. I think we are pretty similar at the moment," said Lorenzo. "Also Sepang is just one track. Let's see what happens at Texas and Jerez."

Best lap time aside, Lorenzo delivered impressive consistency and strong race simulations at Sepang. Pedrosa has so far stuck to short runs.