Brian Vickers has been told he will not race again in 2013, after medical tests detected a blood clot in his right calf that will force him to undergo treatment via a round of blood thinning medication.

NASCAR will not allow Vickers to compete while on blood thinners, because of the risk of haemorrhaging in the event of an on-track accident.

Vickers revealed that he had been placed on the medication by Dr. William Downey after a Monday morning examination on his right leg discovered a small blood clot in his calf region. He was immediately stood down from active competition status.

Vickers has been driving the #55 Michael Waltrip Racing car in 2013, initially as relief to the part-time Mark Martin and then full-time since Martin departed to take over the #14 car for the injured Tony Stewart for the remainder of the current season, after Stewart broke his leg in a racing accident in August. In 22 races with MWR in 2012 and 2013, Vickers took five top five and ten top ten finishes, including a victory on July 14 at New Hampshire Motor Speedway.

Michael Waltrip himself had already been due to drive the #55 at next Sunday's race in Talladega, and beyond that MWR co-owner Rob Kauffman said that no decision had been taken yet as to who would replace Vickers in the #55 for the remaining four races of the season. "We were just informed this morning and our concern is for Brian's health," said Kauffmann. "Anything else will be worked out in due course."

Vickers has been scheduled to participate in a test day at Charlotte Motor Speedway on Monday, but his place was taken at short notice by Brett Moffitt. He has also been competing full time in the Nationwide Series for Joe Gibbs Racing and is currently in eighth place in the championship with three races remaining in the current season. JGR did not have any initial comment on a stand-in, and in any case the Nationwide Series is currently on hiatus until November.

It's certainly a worrying development for Vickers, who was forced to miss most of the 2010 season with blood clots found in his lungs and his left leg while driving full time for the now-defunct Red Bull Racing Cup team, and which required heart surgery as part of the treatment he received. However, the driver seemed confident that this latest news would not be of any major medium- or long-term concern.

"If there's anything to be positive about with today's news it's that this is only a temporary setback," said Vickers. "The timing for this is never good, but I'm glad we'll get it out of the way now and be ready to run for a championship with the [#55] in 2014," he added, insisting that his physicians are confident he will be able to resume activity before the start of next season where is due to run a full-time Cup campaign in the #55 for the first time.

MWR to scale back to two full-time teams in 2014

The news about Vickers' medical condition came on the same day that Michael Waltrip Racing staff learned that the team would have to cut back to a two-car full-time line-up in 2013 in the wake of the loss of key sponsor NAPA following the Richmond race manipulation scandal.

The #56 car that formerly carried primary sponsorship from NAPA will become a part-time operation, and team co-owner Michael Waltrip reportedly told employees affected by the approximately 15 per cent downsizing in staffing that they were free to seek alternative employment with immediate effect, according to The Associated Press which initially broke the news.

"Today was about doing what we had to do not what we wanted to do," said team co-owner Rob Kauffman. "It was important to let those whose jobs were affected know as early as possible, and a majority of those will remain with MWR through the end of the season."

"Our goals for the reorganization were twofold, firstly to improve the competitiveness of our race teams and, secondly maintain a stable organizational structure," Kauffman added. "The team's focus has been to find that last one percent needed to move from Chase participant to Cup champion. This realignment will get us closer to that last one percent."

"We are confident that with two teams and a very active test team, our competiveness will take a step forward," said Michael Waltrip, Kauffman's co-owner and a driver for the team. "We will also continue to do a great job for our partners off the track, which has always been a cultural staple for our organization.

"Rob and I deeply appreciate everyone who has helped build MWR into a race winning team and we are dedicated to continuing our pursuit of excellence on and off the track," Waltrip added, stressing ongoing support from engine providers Toyota and from the remaining stable of team sponsors including 5-Hour Energy drinks and retail chain Aaron's.

It's not known whether the current driver of the #56, Martin Truex Jr., will stay with the team in any capacity in 2014. It's been widely rumoured that Truex - embarrassed to have been the innocent party at the centre of the team's efforts to rig the Richmond race result in an attempt to get him into the championship play-offs - is evaluating his options and meeting with other interested teams such as Furniture Row Racing who are seeking a replacement for Kurt Busch next season.

MWR expect to continue full-time operations with Clint Bowyer in the #15 and Brian Vickers - assuming he recovers in time from his latest medial issues - in the #55.