Lampard was explaining the absence of the 26-year-old Czech Republic international striker, who is reported to be an £11 million transfer target for Leeds United, from the Rams' pre-season training camp.
Vydra, who is the highest earner at the club, is thought to have been told he can leave Pride Park this summer if his valuation is met as Derby look to reduce their spending.
Leeds have already seen a £7 million offer rejected, while West Brom also thought to be monitoring the situation so, following the news that Vydra had been left out of Derby's squad that travelled to Tenerife for some warm-weather training, Lampard was asked why.
Lampard, 40, told The Derby Telegraph newspaper: "Vydra had a small injury which has been dealt with. He hasn't trained properly. It was much better for him and the medical team to get one-on-one work back at the training ground. So, he has got a week there to get himself ready and we hope he will then be ready to join in with the rest of the lads. There was no point in him travelling with 25 of us here (to Tenerife) as there is a lot of work to be done across the board. And similar with Chris Martin [who was also left behind]. He has had some issues. Again, he will have his own programme. He will be able to build up on the work he needs to do and hopefully we will go back to two players that will be fit and ready."