José Mourinho says he has told Marouane Fellaini to “shut up” and accept Manchester United’s contract offer before the seriousness of the midfielder’s knee injury is diagnosed.

The manager was smiling as he recounted the conversation but behind his jokingly delivered line to Fellaini appeared to lie a serious point. Fellaini’s deal ends on 1 July and the 30-year-old wants a sizeable increase on a salary thought to be around £120,000 a week. He suffered a knee problem that limited him to seven minutes as a substitute in Wednesday’s 2-0 defeat away to Tottenham.

“I told him yesterday: ‘Sign the contract and shut up,’” said Mourinho. “I told him: ‘Don’t gamble too much. Sign the contract before you know the extent of the injury.’ It is not an ACL, a complete rupture of any structure of the knee. But we need him, the Champions League is arriving [on 21 February] and lots of tough matches to play and probably we are going to lose him for a few weeks. Two, three, four or five, I cannot say at the moment.”

Mourinho has conceded the title to Manchester City for the first time but wants their raising of the bar to be the “click” that drives his team on next season. Mourinho draws inspiration from United’s response after his Chelsea side won the Premier League for a second successive season more than a decade ago.

“I always remember when Sir Alex [Ferguson] said in 2005-06, when we won the second title with Chelsea: ‘We need to improve a lot because they have raised the bar to such a level,’” Mourinho said. “They [Chelsea] won two titles in a row, the second title was easier than the first and then the biggest manager in the Premier League said Man Utd needed to improve a lot. That was the click for the improvement of the team.

“In 2006-07 Man Utd won the title back. It has to be like that [for us]. That is why every match until the end of the season is important for us. It is not just about the points and finishing in the top four, which is important. Try to finish second. Try to play the best we can and improve the players individually the best we can and be the best possible team at the end of the season.

“Then we must try to start next season in a good way, like we did this season, but try to be consistent and try not to lose points like we did this season in some matches where we shouldn’t.”