He has found the net in the last two games –his first goals at senior level – and boss Colin Calderwood rang Latics yesterday to sort out the extension.
Latics are happy with the arrangement as they want the 19-year-old to get as much league action under his belt as possible.
At present Vieira is unlikely to get that with Latics, with a number of more experienced strikers ahead of him in the pecking order.
During his initial spell with the Cobblers, he has started three games and come off the bench in two others.
He was also a substitute in the FA Cup tie with Manchester United last month but didn't make it on to the pitch.
The deal for the second month was completed in time for him to play in tonight's game at Darlington, and it runs until March 17.
Latics see Vieira, who was 19 last Friday, as a player for the future rather than in this season's battle in the upper reaches of Division One.
Since signing a three-year professional contract in August, he has been in the first team squad just twice as an unused sub.
Manager Paul Jewell already has plenty of options up front, with Nathan Ellington and Jason Roberts the current first choice pairing in attack.
Andy Liddell and Lee McCulloch are backing them up from the bench, and then there's Neil Roberts who hasn't even been able to make the 16 in the last three games.
Jewell is content with that competition and pleased to see top scorer Ellington bang in form having struck six goals in the last eight matches.
He said: "The Duke's partnership with Jason Roberts is looking dangerous and we have some great competition up there.
"On Saturday we were able to bring Liddell and McCulloch on towards the end which shows the strength in depth.
"The Duke is a confidence player, he is improving all the time, and he gets more than his fair share of goals.
"He has got a lot in his locker, and while he can drive you up the wall at times, he is getting better and better."
Meanwhile, Latics pair Gary Teale and Neil Roberts could find themselves in opposition at the Millennium Stadium tomorrow night.
Teale was named in the Scotland squad last week for the friendly against Wales, while Roberts got a late call-up to the Welsh party yesterday.
Winger Teale took part in his first training session with the Scots at Barry Town yesterday, and hopes to win his first cap.
But Lee McCulloch will have to wait a little longer for his chance after being placed on stand-by for the game.
Manager Berti Vogts decided against calling up reinforcements despite a couple of pull-outs over the weekend.
Source : Wigan Evening Post.