Gordon Strachan says he should have called Liam Cooper up for Scotland's World Cup qualifiers earlier this month and did not want to make the same mistake again.

The Leeds United defender has been included for the national side's closing 2018 World Cup qualifiers against Slovakia and Slovenia in October.

He is the only new face in the squad as Russell Martin, Tom Cairney and Steven Naismith drop out.

Strachan has not picked Cooper, who has yet to make his senior debut, since March's qualifying win over Slovenia but said he should have been a part of September's vital victories over Malta and Lithuania.

"He's playing well in a winning side," the manager explained.

"He's a big influence, he's captain now and that's big progress for Leeds and himself.

"I probably should have had him in the last squad to be honest so I made sure I didn't make the same mistake again."

Meanwhile, Strachan confirmed he chose to leave out Norwich City duo Martin and Naismith due to their lack of match action this season.

"Since they left us the last time I've spoken to the two lads and they're really positive in terms of where we want to go as a squad," he continued.

"They would like to be included but at the moment they know, and I know, that not being in the Norwich squad is not conducive to what they normally bring to our squad.

"We will miss them in terms of professionalism and enthusiasm but we have to weigh that up with taking guys away for eight days and maybe not being stripped.

"I spoke to them and they're in agreement with me that's it's probably best. But they want to be on call, they'll be ready in case they are needed."