Marc Marquez struggled with an issue with the brake discs on his Repsol Honda as the second Sepang test got under way on Monday, which dogged him throughout the day.

The reigning MotoGP world champion, who set the fastest lap ever at Sepang during the opening test a fortnight ago, ended the day sixth quickest with a time of 2m 01.190s.

A disappointed Marquez said: "Today was a slightly strange day and not very productive, because I had some difficulties with the front brakes from the first run-out. We focused on improving that aspect of the bike and could only do runs of one or two laps.

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"That took up the time we had allotted for trying other things and prevented us from progressing. Now we will try to find the source of the problem and tomorrow we hope to continue with the testing plan."

Marquez ran off the track on several occasions and was mystified as to the cause of the issue, explaining that his RC213V had been unchanged from the previous test.

"Today was not very good for me because we didn't try anything and just concentrated on the brakes to try to avoid this problem and it was really strange because the bike was the same as when we finished in the [last] test and it was perfect," he said.

"We will try again tomorrow and try to change everything to try to change this problem. The problem is at some braking points it was braking well but at other brake points the level was going down completely and I couldn't lift up the bike.

"It was not constant but it was dangerous and many times I went off the track. We talked to Brembo, but nobody has this problem at the moment and tomorrow we will try to find a solution," added Marquez, whose time was 0.776s down on Movistar Yamaha rider Valentino Rossi's quickest lap.

"We tried the two bikes and we tried a completely new system with the brakes but it was the same. My riding style is the same and it is difficult to understand."

Marquez revealed that he has a number of new components to test aimed at improving the character of the engine and grip level, but was reluctant to elaborate further.

"We have some new items to try on the chassis side to improve the grip level and some set-ups and something on the engine to improve its character," he said.

"Today the programme was to try some of these new items but we couldn't; tomorrow we will try these new items but first of all we need to improve the front brake feeling and then we will try to continue our plan.

"[We have] something to improve the grip and something to improve the character of the engine but I will not say exactly what!

"Honda has brought something that we will try tomorrow or on the third day to improve edge grip and exit grip," he added.

"The tyres are exactly same as last year so for the last test I was really strong on one lap but you always try to improve on that aspect."