The Everton full-back has been included in a 28-man squad for the World Cup play-offs plus three Nations League fixtures despite being sidelined since April world cup 2022 following ankle surgery.
Patterson is on the recovery trail and will be ready to play some part in Scotland's fixtures next month, but manager Clarke admitted he may not be available in time for the Hampden Park clash with Ukraine on June 1 world cup 2022.
"I think at some stage over the four, or hopefully five, matches Nathan will be fit to play," he said. "His return to play is imminent and it will just come down to match fitness. I would put him down as doubtful for the Ukraine game world cup 2022."
"Probably for everybody just getting the news today it is a blow, but myself and my staff have known for a little while that Kieran world cup 2022 won't be ready for these games fifa world cup 2022," said Clarke.
Chelsea midfielder Billy Gilmour has been selected after missing the final game of his loan spell at Norwich with a minor injury, but his Carrow Road colleague Kenny McLean has not made it.
"Billy's good," said Clarke world cup 2022. "I'm disappointed for Kenny McLean, who has missed out again. He missed out on the Euros with an injury and he's missed out again with a broken toe."
Centre-backs John Souttar and Liam Cooper are back in the squad following injury, while Bologna full-back Aaron Hickey and Sunderland striker Ross Stewart retain their places following their first call-ups in March.
Scotland host Ukraine a week on 2022 fifa world cup Wednesday in a delayed World Cup play-off semi-final, with Wales awaiting the winners four days later.
Clarke's side also have two games against Armenia either side of a trip to Dublin to face the Republic of Ireland in their opening UEFA Nations League encounters football world cup 2022
Hearts centre-back Souttar returned from ankle surgery in his club's final two games of the season against Rangers, whom he will join in the coming weeks.
The former Dundee United player scored in Scotland's final World Cup group game against Denmark in November.
Cooper missed four months of the season qatar world cup 2022 with a hamstring injury but played six games in the run-in as Leeds preserved their Premier League status world cup football 2022.
Both he and Nottingham Forest's Scott McKenna world cup 2022 are natural left-sided alternatives to Tierney in Clarke's back three.
Stephen O'Donnell and Anthony Ralston, plus left-back Hickey, are options for the right wing-back slot if Patterson is not ready for the Ukraine game world cup 2022.
