Sunderland boss Mel Reay gives a team news update ahead of Southampton test
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McPartlan, who came through the Manchester City academy, joined last week following a spell at Louisiana State University and made her debut from the bench in the 3-1 defeat to London City Lionesses.
Sunderland's head coach says the midfielder needs time to readjust to the English game but expects her to be involved this weekend.
"We're just trying to bring her up to speed, she's been out of the country for four years so it's about getting used to the game over here again - it's very different," Reay said.
"She's a good addition, a big, strong central midfielder who likes to break the play up and get on the ball. It's different to what we have and adds that depth and competition.
"Brenna has got good pedigree in the game and so she's technically very good. I was really happy with the window, we feel we've covered all positions by adding four good players to the squad."
Sunderland have no fresh injury worries ahead of the game, with a late decision set to be made on Neve Herron's availability.
Herron missed last weekend's defeat having picked up an injury against Manchester United in the FA Cup a week previous.
"Neve is back in some non-contact training so she'll report back in today and we'll see if she's available, that one will be a late call," Reay said.
"She'd burst a blood vessel behind her pupil, so you couldn't see it to look at, but she was having some issues with blurred vision. "She's had the treatment she needed but we'll not rush her, we'll see."
Sunderland will be facing a Southampton side enjoying a very successful first campaign in the Championship, currently sitting third in the table and just four points off London City Lionesses and Bristol City at the top.
They beat Reay's side 1-0 in the return fixture, but that was a game in which there was little between the two sides.
Sunderland's head coach is keen for her side to get back to their best and build on a previously strong start to 2023 back on home turf.
"We knew it was going to be a tough game at London City but I actually think we started really well, we had some good opportunities in their box," Reay said.
"We just had a crazy eight minutes where we've leaked three goals and given ourselves an absolute mountain to climb. It could have gone the other way but fair play, we got a positive reaction in the second half and we've been able to reflect on the lessons learned this week.
"It's been a good start to the year and I think that's why we were disappointed, we'd just slipped from where we were trying to get to, but hopefully it was just a blip and we can put it right on Sunday.
"They're well organised, they don't score a lot but they don't concede many at all. They're a good, well-organised team and so we've got to be at it and we've got to be able to unlock doors."