Glock has managed only 16 laps in two days of testing at Jerez
The new Virgin team have been forced to stop running their car following a front-wing failure at this week's test.
The front wing fell off the car after driver Timo Glock had completed only 11 laps at Jerez in southern Spain.
Technical director Nick Wirth said the cause of the failure had been identified and that the team planned to continue work on Friday.
Glock's best time before Virgin ended their running was more than 10 seconds off the fastest lap of the day.
Glock had done three short runs when the problem occurred about an hour and a half into the second day of the four-day test.
Wirth said in a team statement: "This morning we experienced a front wing mounting problem which caused the wing to come off the car at the beginning of a run. The cause has already been identified.
"Unfortunately, we're missing one or two spare parts which will hopefully arrive this evening, so we won't be able to run for the rest of the day.
Buemi's Toro Rosso set the pace for much of Thursday
"In the short amount of running that we've achieved so far, we are very encouraged by what we've seen and we have gathered some vital aero data which is very much in the range of what we were predicting.
"We look forward to resuming the programme tomorrow morning."
Virgin also managed only limited running on Wednesday, when the late arrival of new parts meant Glock did not go out on to the track until the afternoon.
He managed only five laps before the team ended his work, saying they wanted to ensure the car was ready for a full day's testing on Thursday.
Virgin are one of four new teams to enter F1 in 2010, and are the first to get their car on to the track.
The new Lotus ran for the first time in secret at Silverstone on Tuesday, and will join the other teams for the second of the two Jerez tests, which starts on Wednesday next week.
US F1 and Campos have not run their cars.
I am very happy with how the day went - I managed to complete a lot of laps which is very precious to me
US F1 are expected to do their pre-season running close to their base in Charlotte, North Carolina.
There are question marks over Campos's participation as they struggle to raise the required funding.
Kamui Kobayashi's Sauber set the fastest time of the day, recording a one minute 19.950 seconds lap with a run late in the afternoon session.
Underlining how difficult it is to draw any conclusions at all from this test, that time is more than two seconds slower than was set in the F1 young driver test days at Jerez in December.
Toro Rosso's Sebastian Buemi was next quickest, setting his 1:20.026 in the morning.
He was followed by Jenson Button's McLaren (1:20.618), Williams's Nico Hulkenberg (1:20.629), the Force India of Vitantonio Liuzzi (1:20.754), Mercedes's Michael Schumacher (1:21.083), Ferrari's Fernando Alonso (1:21.424), Renault's Robert Kubica (1:22.033), Red Bull's Mark Webber (1:22.043) and Glock.
Alonso and Schumacher concentrated on doing runs of lots of laps, with the Spaniard running 48 laps consecutively - about two thirds of a race distance - and setting a 1:21.9 on his final lap with worn tyres.
Schumacher said: "I am very happy with how the day went today even if we could not finish our schedule completely due to red flags.
"However, I managed to complete a lot of laps which is very precious to me.
"A new car, a new team and new conditions, therefore our first goal has to be to make the car reliable.
"Days like today help massively in that respect, especially as the weather forecast for the next few days isn't looking quite so rosy. I felt very comfortable driving the car and it was good fun today."
Webber completed two days running for Red Bull, who launched their car on Wednesday, and will now hand the wheel to 2009 runner-up Sebastian Vettel for the remaining two days.
"We've had a few little niggles here and there with reliability, but despite that we've managed to complete quite a few laps with the new car," said Webber.
"We've had one wet and one dry day and learned a lot on both. We've still got quite a bit of testing to go before we get to Bahrain, which we're going to need to continue to understand the car and keep finding performance."
It is all but impossible to judge the relative performances of the cars at this year's winter tests because teams do not release information about how much fuel they have on board.