Swansea City are waiting to discover the extent of Stephen Welsh's knee injury after the centre-back was helped off during their painful defeat at Portsmouth.

Swansea missed the chance to return to the top of the Championship as they were beaten 3-1 following a dramatic climax at Fratton Park on Tuesday.

The prospect of losing the influential Welsh only added to Swansea's misery after Vitor Matos' team slipped to fourth in the table courtesy of a third defeat in their past four matches.

Welsh was injured in a heavy challenge by Ebou Adams which saw the Portsmouth midfielder booked.

When asked whether Scotland international Welsh's problem could be serious, Swansea head coach Vitor Matos said: "Of course there is that possibility, but let's first have the scan and then speak about it."

Welsh joins a growing injury list which already features long-term absentee Cameron Burgess, leaving Swansea light on options in defence.

Swansea are also without wingers Moussa Yeo and Ronald, while midfielder Stephen Eustaquio was not involved against Portsmouth after coming off in last weekend's win over Blackburn Rovers with a groin problem.

Another wide player, Eom Jisung, was another absentee at Fratton Park after suffering what the club described as a contact injury during the Blackburn game.

The various fitness issues have not helped a Swansea side who are losing momentum after their spectacular start to the season.

They had looked on course for a draw at Portsmouth after Zan Vipotnik's 85th-minute penalty made it 1-1, and missed a golden chance to go in front when Ross Stewart hit the bar three minutes later.

After Portsmouth responded with two stoppage-time goals to claim victory, players and staff from both clubs clashed in the centre circle after the final whistle.

Matos said he was unsure what sparked the melee because he was "already inside".

But he added: "Let's say it is not an easy place to come and try to hold the emotions, especially with how the game was.

"It's more a situation for the refs to control. It was quite harsh in terms of decisions I would say. It was an emotional game – everyone quite emotional.

"It was not easy in the first half losing a player with a tackle. Then I would say harsh decisions, really on the limit in terms of cards."

Former Cardiff midfielder Adams was fortunate to escape a second yellow card before half-time when he tripped Filip Lissah on the edge of the Portsmouth penalty area.

Pompey, meanwhile, felt hard done by over the decision to rule out Marezi's tap-in - when the score was 1-0 - for a foul on Jenson Seelt by Adrian Segecic.

Swansea will look to respond to the Portsmouth loss at Birmingham City on Saturday, in their final game before the season's second international break.

The Blues replaced Swansea in second place in the table courtesy of their 3-0 win over Millwall on Tuesday.

"It's a hard league, so many games to come," Matos said.

"We need to stay stable emotionally because it's important for us that we focus on what we need to improve."