Ryan Leonard is set to be out for “a number of weeks” with the knee injury he suffered in Millwall’s 2-1 victory over Leeds United before the international break.
The former Southend United and Sheffield United midfielder went for a scan last Tuesday.
And Lions caretaker manager Adam Barrett admitted Leonard’s absence is a blow as the club’s most expensive signing has been one of the standout performers of late.
“It is his lateral side,” said Barrett. “I think it is a grade two and unfortunately Ryan will be out for a number of weeks.
“He has got to see a specialist this week and they will determine how long he is in a leg brace, and that in turn will determine how long he will be out for.
“It is really disappointing for all of us, we haven’t got a big squad either.
“It’s one of those things. He made a tackle and it just seemed to open the knee up.
“We’ve got players who are good enough there to fill the spot and make sure we’re right for the weekend.
“Ryan has started to produce some of his best performances recently.
“He came to a new club, it was a different environment and sometimes it takes time. He started off really well with us last year.
“I know Ryan really well and I know what he can bring – he’s got great energy, he covers a lot of ground. He mops a lot of stuff up, he does a lot of work that people might not appreciate or see.
“Sometimes it takes time to adjust. The second half of last season was difficult for everyone with the situation we were in.
“But recently Ryan has shown what a good player he is. He gave us great energy against Leeds and it was disappointing to see him go off, but Shaun Williams came on and did a fantastic job for us.”
The only other injury doubt for Millwall ahead of Saturday’s derby at Brentford is Jiri Skalak. The Czech Republic winger has been out with a heel and foot problem since the 4-0 loss to Fulham on August 21.
Brighton loanee Jayson Molumby is set to be back in international action for the Republic of Ireland U21s in their Euro UEFA qualifier in Iceland tonight.
Molumby started last Thursday’s 0-0 draw with Italy at the Tallaght Stadium. Ireland are four points clear at the top of Group A but have played two more matches than the Italians and one more than second-placed Iceland.
Jon Dadi Bodvarsson’s Iceland were due to play Andorra last night. The striker was a second-half substitute in a 1-0 home reverse to France on Friday night – Olivier Giroud’s penalty settling the contest.