Victor Wanyama has returned to London from Tottenham's pre-season tour of the US as Mauricio Pochettino's midfield injury crisis worsened in the defeat to Barcelona in the early hours of Sunday morning.

Spurs lost 5-3 to the Spanish champions on penalties after a 2-2 draw but more worrying than the result was a hamstring injury to Moussa Sissoko – the fourth player to be injured on the trip after Wanyama, Erik Lamela and youngster Tashan Oakley-Boothe.

After the game, Pochettino revealed Wanyama has flown home for treatment after suffering a recurrence of the same injury that ruled him out for four months of last season in training last week.

"We need to assess Sissoko tomorrow and in the next few days to see what happens," Pochettino said at the Rose Bowl. "He felt his hamstring but we hope it's a minor injury.

"Erik felt his muscle after [the 4-1 win over] Roma, a minor injury and he's still here with us. We hope we can play against Milan [in Minnesota on Tuesday].

"Victor and Tashan [Oakley-Boothe] are back in London because they need to see the doctor there. We need to assess in the next few days and see what happens."

Spurs trailed 2-0 at the interval to goals from Munir El Haddadi and Arthur before they rallied against a much-changed Barca side in the second half, scoring through Heung-min Son and Georges-Kevin Nkoudou.

Youngster Anthony Georgiou was the only player to miss in the shootout, but after the game all the attention was on Spurs' missing midfielders.

With World Cup semi-finalists Eric Dier and Mousa Dembele not due back in training until August 6 – five days before their opening League game – and Harry Winks and Joshua Onomah also back in London working their way back from injury, Pochettino is now without seven centre-midfielders.

He insisted the situation would not force Spurs to enter the transfer market and said the club continues to work towards making a first summer signing.

"We're sure to see what happens in the next few days," he said. "If you say we need to sign [players], maybe, but with or without injuries.

"To bring some players with quality to help us achieve what we want was our target after last season finished. With or without injuries, we are working [on transfers].

"Yes, of course I'm relaxed. I've a lot of experience in football now. After many years, I know nothing is going to change if you're in a different situation. You need to be relaxed, working hard, my focus is to work the team."

In the meantime, Pochettino gave another start to 20-year-old Luke Amos against Barca, while 17-year-old Oliver Skipp impressed after coming off the bench at half-time.

"It's amazing to give the possibility to players like Luke Amos and Oliver Skipp – they were fantastic. They played against Roma and tonight – an amazing experience for them.

"That experience is massive We need to take positive things in a negative period."

Pochettino was asked about the possibility of re-signing Gareth Bale. "That is not realistic," he said.