Front row duo Sourgens and Black will get a first ever taste of life as a Worcester Warriors player when they check in to the club on Wednesday.
Grove will also return to full training after his eye catching exploits with Scotland in the IRB Nations Cup in Romaina.
"We have given the whole squad a few days off at the start of this week to recharge the batteries before we are back in on Wednesday with some new faces," said Director of Rugby Ruddock.
"Alex (Grove) will resume training with us after his successful spell with Scotland A in Romania and he will be joined by Adam Black and Olivier Sourgens who all report for pre-season.
"Both Olivier and Adam started their contracts with Warriors in the first week of July, but have been given extended time before return after longer playing spells with previous clubs.
"All three players will be expected to fulfil a comprehensive series of fitness tests during the first day back at the work place.
"As they have all been advised of this in advance, I'm sure they will have been putting in the necessary preparatory work. It's straight into work for them.
"The only players who will not be back are Netani Talei, who remains away from pre-season after action with Fiji in Pacific Nations Cup, and Graham Kitchener who will return next week after an intense spell playing for England Under 20s in the IRB Junior World Championships in Japan."
