Giroud has not played for title chasing Arsenal since scoring in their 1-0 win at Newcastle United on Dec. 29, the tall Frenchman forced to rest after suffering a blow to his ankle in a tackle by defender Mike Williamson.
"He played the whole game at Newcastle with an open ankle and without complaining. And when I took him off, he didn't want to come off. He needed five stitches," Wenger said in quotes carried by British media on Monday.
"He was a bit tired recently but now he is refreshed, he is back, and I am sure he will have a major impact on the second part of the season."
Theo Walcott and Nicklas Bendtner both contributed late goals in the 2-0 win against Cardiff City on Jan. 1 in the absence of Giroud but the Dane injured his ankle in the process of scoring and is expected to miss a few weeks.
England winger Walcott played as the central striker in the 2-0 FA Cup success over arch rivals Tottenham Hotspur last time out but his game ended early with a serious knee injury which will rule him out for the rest of the season.
German Lukas Podolski has recently returned to action following a hamstring problem but Wenger has been reluctant to field him as the central striker in Arsenal's attacking three and acknowledged he needed reinforcements to maintain their title challenge.
"That is why we are out there," Wenger said when asked about the risks of trying to compete for trophies with his current squad.
"Last summer (close season) I looked for a striker that could play with Giroud and without Giroud. In my mind it was not absolutely to replace Giroud, it was to play with or without him."
Giroud started his second season in north London with three goals in his first three games in all competitions but has found them harder to come by in recent weeks.
His winning goal at Newcastle was his eighth Premier League goal of the season but his first in seven matches for the club since scoring both in a 2-0 home win over Southampton.
Wenger said the 27-year-old, signed from Ligue One side Montpellier in July 2012, was crucial to Arsenal's style of play and his contribution went far further than scoring goals.
"He has qualities that the rest of the squad has not got. He always gives us that strength," said Wenger, whose side can return to the top of the table with a victory on Monday.
"We have small players who combine quickly, so to find someone who can hold it, keep the ball, make some room for other players, he does that very well. He gives us a very good balance."
Giroud scored after only six minutes when Arsenal last met Villa on the opening day of the season, but Paul Lambert's side struck back with three unanswered goals to grab the three points and leave the home fans at the Emirates booing Wenger.
Villa, though, have won once in their last six Premier League outings and were beaten at home by third tier Sheffield United in the FA Cup last time out.
They are 11th in the table but only six points ahead of bottom side Crystal Palace and Lambert said he felt the pressure.
"I don't sleep great, I don't eat great. The usual stuff," he added. "It is just the life of a football manager."
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