Laszlo is keen to sign the former Rangers youth player on loan along with McLeod, although the Charlton striker's arrival in Edinburgh has been delayed.
Hearts announced on Monday morning that MacLean was on trial and would be assessed by Laszlo over the course of this week.
But the Hearts manager has already made his mind up to sign the former Sheffield Wednesday striker as well as McLeod, whose scheduled appearance at training was postponed until after Charlton's League One derby against Brentford on Monday.
Christian Nade is the club's top-scoring striker this season with two goals and Laszlo has made no secret of his desperation to add firepower after the club failed to land any of his striking targets in the previous two transfer windows.
"I know both players, they were on my list to bring to Hearts last summer and we have a big chance to get them on loan," Laszlo told the Edinburgh Evening News.
"I want to bring them here for half a season. I don't like to have a trial and then make a decision. I already have my decision in this direction.
"We want to see that they are in good condition but they have been training with their teams and I spoke with their clubs. Both players said they would like to come to Hearts."
MacLean's arrival at Hearts is as a blow to Aberdeen manager Mark McGhee, who tried to sign the 27-year-old in the summer.
McGhee has recently stepped up efforts to sign MacLean and Argyle team-mate Jim Paterson on pre-contract deals but is unlikely to be able to afford an immediate transfer.
After four substitute appearances with Rangers, MacLean joined Sheffield Wednesday after hitting 25 goals in a season-long loan at Scunthorpe.
The striker netted 35 goals in three seasons at Hillsborough before signing for Cardiff but McLean endured an unhappy spell in Wales before signing for the Pilgrims in a club-record £500,000 deal in January 2008.
However, the Edinburgh-born forward has made only four appearances this season.
Meanwhile, Laszlo fears he will be without right-back Craig Thomson for Sunday's Edinburgh derby.
The 18-year-old has a knee ligament strain which will rule him out of Wednesday's SPL clash with managerless Motherwell at Tynecastle, and probably the trip to Easter Road.
Thomson was seen by specialists last week and will undergo a scan this week.
"It is not a serious problem, but we must make sure that Craig is fit and so we cannot push him in the game against Hibs if he is not ready," Laszlo told Hearts News.
"Our medical staff will assess him and we'll do our best to get him fit as soon as possible."