Scotland 1-2 Russia: Andy Robertson says loss is among his 'most disappointing'
Scotland captain Andy Robertson has described Friday's home defeat by Russia was "one of the most disappointing" results of his career.
The 2-1 loss at Hampden Park means Scotland have a mountain to climb to salvage their automatic qualification hopes for Euro 2020.
Steve Clarke's side are now six points adrift of second-placed Russia with five matches left in Group I.
"It's because of how much was on the line," said defender Robertson, 25.
"We had a chance to go level with them and that would have opened this group right up.
"Russia are a very good team, so it's probably not up there with the Georgia [1-0] and Kazakhstan [3-0] results or the Lithuania draw at home - because they're teams we should have been beating - but we knew how big this game was and we wanted the three points."
Scotland host the might of Belgium, the world's top-ranked side, on Monday (19:45 BST) knowing defeat could leave them nine points behind an automatic qualification spot with just 12 points available.
"The worrying thing is how far we are behind Russia," added Liverpool left-back Robertson.
"We believed we could have been the team to compete with them and now they're six points clear. That's going to be hard to get back but we need to try.
"Unfortunately, we have Belgium at home. There's now no other option than to get a result.
"If we don't get a result on Monday, I think it's going to be verging on impossible to get through this group."