Arsenal's Wojciech Szczesny was promoted to Poland's starting line-up for Tuesday's 2-0 defeat to England, with physio Jacek Jaroszewski insisting that Boruc was omitted due to a hamstring problem.
Boruc was reported to have suffered the setback against Ukraine, and the 33-year-old posted a photo of what appeared to be himself with his right leg in a protective support.
But Pochettino insists there is no problem with the former Celtic goalkeeper and expects him to start Saturday's trip to Manchester United.
"Artur is OK," the Saints boss said. "There is some news that has come out, which is not true, regarding his fitness. He is fine.
"He has been training for three days. He has been training well and we hope that he will be perfect for Saturday's game."
Pochettino also played down concerns over Luke Shaw's fitness after the teenage left-back missed England U21 duty through illness.
"The last few days he has been training well, he has been OK," the Argentine added. "We hope that he will be physically fit for the game on Saturday against Manchester United.
"The rest of the squad arrived back from the international break. The only one that has not arrived yet is Gaston Ramirez and we think he will arrive on Thursday night."
Ramirez has spent the international break with the Uruguay national team amid speculation that the midfielder is unhappy at Southampton.
The player's agent, Pablo Betancourt, was reported in Italy to have claimed Ramirez likes the chairman, Nicola Cortese, but not Pochettino.
"I don't really have an opinion on what is in the press regarding those matters," said the Saints boss.
"I really don't have a comment on that. I only make decisions based on sports factors, on the performance of the team, for the good of the team.
"I have no preference for any of the 24 players I have available to me. I just make decisions on sports factors."
Borussia Dortmund, Atletico Madrid and Napoli have all recently been linked to the 22-year-old, who signed from Bologna last year for a then club-record fee of £12m.
He was left out of the Saints squad for the 2-0 win over Swansea before the international break, but Pochettino would not elaborate on the reasons for Ramirez's absence.
"I don't want to speak publicly about individual players," he said. "I don't think that's fair. I just make decisions on what is the best thing for the club, the team. I just make decisions based on training and sports factors.
"I try to make the best decisions for my team to win games, to play in a good manner.
"It is always clear that there are 11 starting players, seven on the bench and there is five or six players that have to be left out, so it is a mathematical equation."