Rangers have taken former Premier League players Hameur Bouazza and Mamady Sidibe on trial.
Mali striker Sidibe left Stoke earlier this summer while Algeria winger Bouazza, who was at Racing Santander in Spain last season, counts Watford and Fulham among his former clubs.
Both players were suggested to Rangers manager Ally McCoist by Gregory Dakad, the agent who helped broker Bilel Moshni's move to Ibrox.
McCoist told the club website: "The boys are two players who Gregory looks after and they'll be well known to people who know their English and European football.
"They've just come in to have a look at our place and also for us to have a wee look at them. This is their first day as they came into the city last night.
"They trained this morning and they were absolutely fine. They're obviously not up to the same levels of fitness as our lads are but that's totally understandable.
"They haven't done any pre-season training yet and there's no pressure on anybody. We'll make them feel very welcome and we'll see what happens.
"It would be crazy of us not to take the option to bring other people in and have a look at them after the success we've had with Bilel's trial. Both players have good pedigree."
Rangers have already brought in eight players this summer, but none can be registered permanently until a transfer embargo is lifted in September.
The paperwork for Blackman's move to Home Park on a six-month contract has now been finalised.
The left-back, who was a free agent after being released by SPL champions Celtic this summer, played the first half of the weekend's friendly against Yeovil, having trained with his new team-mates earlier that week.
After the match, Sheridan said: "I think he's a good player; he'll give us a lot.
"I thought he did okay. He hasn't trained much and he's new to the players but I think you could see his ability on the ball.
"He's got to get used to how we want to play and where we want to send players when they're in deep areas because we're all different. Different managers want different things.
"I'm sure in another week he'll fit in with team shape and how we want to play and take it on board because he's only been here for a day or two.
"I've seen him play a few times and I think he's an excellent footballer. That's why I've brought him here."