Steve Clarke says nobody should doubt his Scotland players despite a torrid run of form that stretches for more than a year without a competitive victory.

Saturday's 2-1 Nations League defeat to Croatia in Zagreb means the Scots have won just one of their past 15 matches - a friendly with Gibraltar.

As his side prepares to take on Portugal at Hampden on Tuesday, the head coach insists his belief in his players remains absolute.

"It’s a tough moment, no doubt about it, but we believe in ourselves," Clarke said.

"After 20 years in the international wilderness this group has got to two major tournaments and been promoted to the top level of the Nations League, so I don't understand why there would be doubts.

"We have to believe in what we are doing and when I look at the players on the pitch, I believe in what we're doing.

"The players understand where we are in the process and they are ready to go again."

"They understand that we are playing difficult opponents and they understand the squad could be stronger.

"I don’t speak about that too much since we have to concentrate on who we have here. We have to go out against Portugal and we know we have to be good at everything we do in the game."

Scotland have lost each of their three Nations League A matches by a single goal, Poland at Hampden, away to Portugal and in Croatia at the weekend.

Clarke says his team will need to "find another level" if they are to overcome the superstars of Portugal and is sure they can take confidence from their performance in Lisbon last month when Cristiano Ronaldo's late goal denied them a point.

One bright spark for Scotland has been the emergence of Ben Doak, who made an impressive first international start in Zagreb.

"We’re already starting to grow the next generation of players," Clarke said.

"As well as trying to be good now, I’m trying to leave a group who are ready to carry on. We don't want 20 years after this group without the success we all want.

"We want Ben to be a talent for the next 15 years, not 15 months, so don't put too much pressure on him.

"He's a young man, he will make mistakes in the game, he will do really good things in the game.

"We need to get the balance right between giving Ben the opportunity to play, which he's more than capable of taking, and protecting him a bit, make sure we don't overhype.

"The most important thing for Ben is that he fulfils his potential."

Uncapped Rangers midfielder Connor Barron replaces experienced Celtic winger James Forrest in a squad missing several regulars.

Barron has been drafted in from the under-21s, who visit Kazakhstan in their final European Championship qualifier on Tuesday.

Nicky Devlin, Andy Irving, Liam Lindsay and Jack MacKenzie were on the bench in Zagreb but were not called upon, with reserve goalkeepers Jon McCracken and Robby McCrorie also unused and awaiting a first full Scotland cap.

Vice-captain John McGinn is among those absent through injury, along with Kieran Tierney, Aaron Hickey, Angus Gunn, Scott McKenna, Lewis Ferguson and Lawrence Shankland.