The Fir Park club confirmed on its Twitter account on Friday afternoon that 26-year-old Ainsworth would be staying in Scotland until the end of the season.
The former Shrewsbury wide man was due to return to the New York Stadium on January 7 but after bagging four goals in his last four outings, McCall was desperate to keep hold of him.
McCall's attention will now turn to persuading Norwegian club Viking Stavanger to allow the Steelmen keep hold of Estonian Anier for longer.
The former Sampdoria youth player has contributed seven goals in 23 appearances for Well but has just two weeks remaining on his loan stint.
McCall is eager to keep hold of him but Motherwell have been told by Viking they will have to dig deep to extend his stay.
The Motherwell manager said: "We have a week to try and find a financial solution for Henri.
"Our chief executive Leeann Dempster and the board are working as hard as they can on some creative ways to find some money but at the moment there is nothing to report.
"If it was just a straight forward matter of taking him on a short loan again it wouldn't be a problem. But I think Viking are looking for us to take him longer. At the moment we are only paying half his wages but if we do take him longer we would need to pay all of his wages.
"But we remain hopeful. Henri is desperate to stay. I had a good chat with him on Thursday and he says he is enjoying his time here and feels settled."
Motherwell have bounced back from the double shock of a William Hill Scottish Cup exit to League Two minnows Albion Rovers and a five-goal mauling by Celtic to notch up five straight wins and reclaim second spot.
They now take on Inverness at Fir Park on Saturday but McCall is not concerned that his players have not received the same kind of praise dished out to the Scottish Premiership's other form teams.
He said: "There is no way we will fall into the trap of talking about second place. We have done absolutely nothing at this moment.
"The greatest achievement we have done is to bounce back from the horrible week we had a month ago. But there is still a lot of hard work to do to get into that top six.
"The focus was certainly on us a month ago when we were knocked out of the cup and they shipped five to Celtic, but that was for the wrong reasons. But after the overhaul we had in the summer, I'm really pleased with the lads. Had it not been for a last-minute goal in the cup I'd be sitting here saying we'd had a terrific season so far.
"That's not been the case but we move on. Aberdeen, Dundee United and St Johnstone, after their run in Europe, have all deserved the plaudits they have had this season.
"But our lads will get the plaudits now having already had the stick. That's the way football is and we will just carry on as we are."
Meanwhile, the club have confirmed the Fir Park pitch will undergo a 9am "precautionary" pitch inspection on Saturday following days of heavy rain. However, Press Association Sport understands the match is expected to go ahead.
Motherwell goalkeeper Gunnar Neilson will return against Inverness after on-loan stopper Dan Twardzik was sent back to Dundee.
Inverness midfielder Ross Draper is suspended after being sent off against Ross County while winger Marley Watkins is a doubt after suffering a dead leg in the New Year derby.
Inverness defender Gary Warren is relishing the challenge of playing in-form Motherwell.
But he has warned his team need to cut out the concession of "sloppy goals" following a poor festive period.
In contrast, Motherwell swept into second place in the Scottish Premiership thanks to five consecutive wins, during which they have scored 15 goals.
But centre-back Warren does not fear Saturday's trip to Fir Park.
The Englishman told his club's official YouTube channel: "It's good as a defender. It means you have to be at your very best.
"It's those type of games you have to look forward to - playing against the best, playing against the best centre-forwards in the league.
"It puts you in a position where you have to be strong and stand up and be counted."
- Sports & Recreation