George North is available for Saints’ Aviva Premiership opener against Saracens at Twickenham on Saturday.
The Wales wing picked up a hamstring injury during the British & Irish Lions series draw in New Zealand, forcing him to head home from the tour early.
He has not featured for Saints during pre-season, but is now fit enough to return.
And Mallinder will have to choose whether to put the player straight back in the squad for this weekend’s big game against the current European champions.
“George North is getting on well,” Mallinder said.
“He’s trained fully today (Tuesday) so he’ll be available for selection.
“He’s up and raring to go.”
But two players who definitely won’t play on Saturday are fly-halves Piers Francis and Stephen Myler.
Myler is still recovering from the knee problem he sustained against Saracens at Stadium MK back in April, while Francis fractured his jaw in the pre-season win against Glasgow.
And Mallinder said: “Piers will be out for a few weeks.
“He cracked his jaw so he’s already mending. It was a week and a half ago now.
“He’ll be back in a few weeks - it’s not a long-term injury.
“It’s disappointing for him to come over and be really looking forward to the start and then get that injury, but he’ll be back in a few weeks.
“Stephen Myler is making good progress and we hoped he would be fit to start the season, but he’s just been slightly delayed and he’ll be fit and ready to play in the middle of September.”
Saints welcomed Australia back Rob Horne and South Africa scrum-half Cobus Reinach to the club this week, with the pair having joined from the Waratahs and the Sharks respectively.
Both concluded their Super Rugby season in July and Mallinder will now consider the right time to throw them into action, with Monday night’s Wanderers game at Sale Sharks seemingly the most likely option.
“They have arrived,” Mallinder confirmed.
“They arrived at the weekend so they’ve been training the past couple of days and we have to make up our mind as to whether it’s too soon to put them in this weekend.
“They are available for selection but if we don’t put them in, we might be seeing them up at Sale on Monday night.
“That’s why these second-team games are really important because we’ve got a squad that has played well during pre-season - the youngsters, the experienced players, the new players joining, everyone has put their hand up for selection.
“We can only select 15 and eight on the bench so these Monday night games will really give us a chance for the other lads to put their hands up and show the coaches they’re ready for first-team rugby.”
Tom Wood is available for selection this weekend after completing his six-week ban for stamping in the final game of last season: the Champions Cup play-off win against Stade Français.
But Wood may also have to wait until Monday night, having not been able to play during pre-season.
Centre Tom Stephenson picked up a dead leg in the win against Ulster last Friday and is a doubt for this weekend.