Slavisa Jokanovic has urged the Fulham owner, Shahid Khan, to keep hold of Ryan Sessegnon and strengthen the squad for a new-year promotion push.

Sessegnon became one of the youngest scorers in FA Cup history – at 16 years and 235 days – with the winner in Fulham’s 2-1 third-round victory at Cardiff.

It was the second time Cardiff had witnessed the promise of Sessegnon, who was born in May 2000, as he scored his first senior goal against them in August. On that occasion he became the youngest scorer in both Championship and Fulham history aged 16 years and 94 days.

Five months on and Sessegnon showed his predatory instincts once more, even if Barrow’s Sean Cato’s effort against Rothwell in 2011 makes him the youngest FA Cup goalscorer at 16 years and 25 days.

The England Under-17 international has been linked to the Premier League’s big guns, with Arsenal, Liverpool, Manchester City, Manchester United, and Tottenham Hotspur all reportedly showing interest in the Wandsworth-born product.

“He’s very good for the project of this football club, he’s one of the most talented teenagers in England,” Jokanovic said.

“I am sure that he is going to be a very important player for us in the future. But he’s only 16 years old, we have to be careful with him, and I prefer not to talk so much about Ryan Sessegnon. He’s a very intelligent kid, he’s working very hard and has to keep going.”

The Florida-based Khan, owner of the Jacksonville Jaguars team in the National Football League, is one of the wealthiest businessmen in the United States.

Jokanovic wants Fulham to invest in the January transfer window and push on with the Cottagers close to the play-off picture. Fulham are in 10th place after a slow start to the season, but winning their game in hand would move them to within three points of the top six.

Asked what he expected of the January transfer window, Jokanovic replied: “It depends on our ambition. I want Ryan Sessegnon, I want one striker and I want one defender.

“We have to try to push the team in the top six. We are past the first third of the season and we have in front of us 20 days still [of the window].

Of Fulham’s win, he said: “I am pleased with this win because we moved the ball well and played with patience. We scored two goals and did enough for third goal.”

Both managers resisted the opportunity to field entirely second-choice XIs in the run-up to crucial Championship fixtures, although Neil Warnock said his hand had been forced on the Cardiff team selection.

Jokanovic kept faith with eight of the Fulham team defeated by Brighton & Hove Albion at Craven Cottage last week. Chris Martin, however, was again absent despite the manager’s insistence that the on-loan Scotland striker will not return to his parent club Derby County.

Warnock made five changes from the side who defeated Aston Villa on Monday, and he admitted he was unwilling to risk players who were nursing injuries. “It’s a sad aspect when you play a weakened team like I have done today,” the Cardiff manager said.

“The FA Cup is a great competition but there are other priorities now. A club like ours cannot afford to go down. We have to make sure we stay up and Bristol City on the horizon is a vital game for us. But today has answered a few questions that we do need reinforcements when we have players out.”

A paltry crowd of 5,199 turned up with many home fans preferring to shun the 11.30am kick-off. The early start time on a Sunday made it difficult for Fulham supporters to travel to south Wales on public transport.

The game was also broadcast live on BBC Wales and Warnock said: “I thought the crowd would be smaller than it was when I saw the kick-off time.”