Isle of Man TT Clerk of the Course Gary Thompson admits there is a possibility racing could be delayed until Sunday following poor weather.
Wednesday's qualifying session was cancelled due to rain and mist around the Mountain Course.
Two practice sessions have been held so far on Sunday and Tuesday, with the Superbike machines having their first run out around the Mountain Course on Tuesday evening in dry but cold and windy conditions.
An amended schedule provides for an extra session today, subject to the weather.
However, the latest cancellation raises the prospect of additional practice on Saturday and possible racing on Sunday.
Thompson told Manx Radio: “People keep saying it is what it is, but it’s becoming difficult actually. The schedule is out for tomorrow and hopefully we’ll get out tomorrow afternoon, because tomorrow evening is looking sketchy.
“I’ve already got a draft schedule for qualifying on Saturday because although it has not been confirmed yet – and we’ll see how the next couple of days go – we could be looking at a Saturday qualifying with a race day on Sunday.”
Bradford’s Dean Harrison was fastest on both his Silicone Engineering Kawasaki Superbike and Superstock machines during last Tuesday evening’s practice session. Harrison set the fastest time of the week so far at 129.5mph.
Manxman Conor Cummins (Milenco by Padgett’s Honda) was second fastest on the Superbike charts ahead of James Hillier, who lapped at 128.07mph on the Quattro Plant/Wicked Coatings Kawasaki.
Michael Dunlop was fourth on his Tyco BMW machine, setting his fastest lap at 126.93mph. The 18-time TT winner was on a flying final lap, matching Harrison’s time as he set the fastest sector times of the evening to Ballaugh, Ramsey and the Bungalow before rolling right off the pace on the run from Cronk ny Mona to the Grandstand.
In the Supersport class, Peter Hickman topped the leaderboard with a speed just shy of 124mph on his Trooper Beer Smiths Triumph.
John Holden and Lee Cain were quickest in the Sidecars at 114.99mph.
Thursday's proposed schedule is now as follows:
11:15: Mountain Road closed
12:30: All roads closed
13:00: Superbike/Superstock/Supersport/Newcomers Qualifying
15:00: Sidecar Qualifying
16:30: Roads open except the Mountain Road
18:00: All roads closed
18:20: Superbike/Superstock/Supersport/Newcomers Qualifying
19:35: TT Zero Qualifying
19:55: Sidecar Qualifying
20:40: TT Zero qualifying
21:30: Roads open except the Mountain Road
22:30: All roads open