Grella's first season in English football has been blighted by a series of injury problems but the Rovers midfielder showed signs of a full recovery after starting in Sunday's vital 2-0 win over Wigan.
Allardyce, who has hailed the Australian international as one of the best passers on the club's books, insists the 29-year-old is almost over his injury nightmare.
The Rovers boss said: "We said we wouldn't throw Vince back in as quickly as we have in the past, and we've been good enough to resist the temptation to make sure he feels 100 per cent fit.
"Obviously from a match-fitness point of view he's still a little short but his game against Wigan will lift him because not only did he play a big part in our victory, he came off without any injuries.
Passing ability"He knows how difficult the Premier League is physically. We've not seen the best of his passing abilities yet and the fitter he gets and the more he copes with the pace, the more we'll see his outstanding passing moves."
Meanwhile, Allardyce insists his decision to take his players on a golfing break to Gleneagles before the Wigan game was vindicated by the result - and has vowed to continue the practice in future.
"Mid-season breaks are an important part of everything I've done," Allardyce said.
"It was only Gleneagles - not Dubai or Tenerife. I think they played a lot more relaxed because they had been prepared in the right way."