• Fears that winger could be out for longer than nine months • Koeman says club may look to sign a player for Bolasie’s position

Everton will send Yannick Bolasie for further tests on his injured knee amid fears their £25m summer signing has damaged more than his cruciate ligament and faces a longer recovery period as a consequence.

The former Crystal Palace winger will miss the remainder of his debut season at Goodison Park after injuring his anterior cruciate ligament during Sunday’s 1-1 draw against Manchester United. Bolasie would be facing up to nine months out for an ACL rupture.

However, initial scans have indicated the damage is not confined to the ACL in Bolasie’s right knee and the 27-year-old may be out for longer. He will visit a specialist in London with a view to surgery next week, although another medical opinion may be required before an operation.

Koeman said: “I’m not involved on the medical side but it is a really big injury. He had a scan last Monday, out of that scan came the news that it’s the cruciate ligaments and maybe something more in his knee but they need to control it now and do a scan again to really know about the state of the injury.”

The Everton manager wanted attacking reinforcements in the January window before Bolasie’s injury, with United’s Memphis Depay and Napoli’s Manolo Gabbiadini both linked. He added: “Maybe it’s necessary that we really need to sign somebody in that position, yes. But we are already looking for players to bring in different positions in the team because we think we need to be stronger from January.”

Everton have won only one of their last 10 matches in all competitions to fall 10 points off Champions League qualification. But, while insisting that remains a long-term target, Koeman admits he never expected the team to be challenging near the top this season. “You know theyare stronger, they invest a lot of money and they are really strong teams,” he said of the current top five in the Premier League. “Those four or five teams normally will fight for the first four positions in the table. In the long term we hope to do that, yes. That’s the project. But not for this season.

“We knew at the start of the season it’s difficult to keep that level because we think we need to improve. We need to be stronger to keep that level. And that shows. After a good period of winning games we’re struggling more now. But that was one of my expectations. I did not expect the whole season to be like the beginning of the season.”

Ross Barkley, Kevin Mirallas, Gerard Deulofeu and Aaron Lennon have all struggled to impress Koeman this season or secure regular roles – Bolasie was ever-present before his injury – with Barkley left on the bench against United.

Koeman, who expects Séamus Coleman to be fit for Saturday’s trip to Watford, said: “Ross is part of the team. He played a lot, he did not play last weekend and that’s the competition we need in the squad. He’s trying to do his best in training every day to show the manager he should play. He is one of the players who needs to bring more productivity and that’s some of the talks we have about what he needs to do to start.

“Sometimes he might not play a tactical reason, sometimes it’s because I expect more from Ross Barkley but I expect more from other players offensively too. He needs to accept it. The best answer you can give is on the pitch. It’s not just about the mentality of the player but about the players’ movement and productivity. They are all reasons why a player may not start.”