Rangers lost 3-2 to Hibernian away from home at Easter Road in the Scottish Championship on Wednesday evening.
The defeat does not meant much for the Gers, who have already won the Scottish Championship title this season and have gain automatic promotion to the Scottish Premiership.
In addition to that, Mark Warburton’s side have clinched the Scottish Challenge Cup this campaign and have progressed to the final of the Scottish Cup.
Johnstone, who played for the Glasgow giants in the 1970s and 1980s and is a club legend, is not overly fussed about the defeat to Hibernian, but he has highlighted his worry about Rangers conceding two away goals quite quickly.
“The worry for me is the way we gave away the goals,” the former Scotland international wrote in The Glasgow Evening Times. “On Sunday, the all-round performance was great. But then we are two down after 18 minutes at Easter Road with two of the silliest goals conceded you will ever see.
“The two central defenders can’t handle a throw-in and the second one is a cross that Wes Foderingham didn’t deal with. Just like that, you are 2-0 down. That is something that we can’t afford to do.”
Rangers’ performance against Hibernian was far from impressive, but it is understandable why it was so.
The Gers have nothing to play for in the league, and on Sunday afternoon, they got the better of Old Firm rivals Celtic in the semi-finals of the Scottish Cup at Hampden Park in Glasgow.