The Scottish Championship side are hoping to bring both former Premier League midfielders to Ibrox this summer.
The Record reports that Mark Warburton flew out to America to set the wheels in motion regarding a deal for the latter of the pair, with talks set to continue next week over a potential move once the Scottish Cup final is out of the way.
However, while Prso admitted that his former Croatia teammate was once one of the most impressive players in the country, he questioned whether the 31-year-old would now be capable of meeting expectations at Ibrox.
"He is very talented player, there is no doubt about that. At his best he was up there with guys like Luka Modric and Ivan Rakitic in terms of his ability. But now? I don't know if he's still at that level because I haven't followed his career in Ukraine or America so I don't want to tell something that may not be true. I prefer not to say," he told the Record.
"But what I do know is he'll need to be 100 per cent fit if he wants to play in Scotland. Believe me if he's not in top shape then moving to Scotland is not a good idea."
Meanwhile, the Record suggests that a potential deal for Barton is moving along much smoother and there is a belief that he could hand the Gers a major pre-cup final boost by signing before the end of the week.
But despite spearheading Burnley's Premier League promotion charge, Prso is once again wary that his old side are taking a considerable gamble going after the 33-year-old.
"It's quite complicated and I just don't want to see Rangers make a mistake and I'm not sure about Barton. I remember when he played for Marseille he found it quite difficult. He was not a top player in France," he added.
While Prso is concerned about whether the pair will make the kind of impact that supporters will expect from Warburton's side, the experience that the pair will bring will undoubtedly help some of the younger members of the squad adapt to life at the highest level.
And with both men being well-known in the English game, their arrivals at Ibrox may enhance the club's reputation further in a country where Warburton has done much of his business in the transfer market.