Paul Lambert will make two of the biggest decisions of the season this afternoon when he assesses the fitness of two of his most influential players ahead of the next stage of the club's promotion challenge.

Grant Holt and Wes Hoolahan have been at the heart of Lambert's two promotion challenges – the first successful, the second on-going.

But with the Championship season approaching its climax, hamstring problems have left major doubts over their participation against Nottingham Forest tonight.

Holt's appears the most serious issue: City's skipper struggled through the final few minutes of the 2-2 draw at Watford on Tuesday, and while Lambert was hoping it was nothing more than cramp, that is almost certainly not the case. The diagnosis revealed to the press yesterday was that it was in the 'hamstring area', leaving him rated 50-50 for tonight.

The good news appears to be that it's not as serious as similar injuries which have hit the City squad this season. Lambert was, as expected, keeping his cards close to his chest at his pre-match media conference yesterday, but admitted it was a case of playing a waiting game.

'We will wait and see,' he said. 'It's minor at the minute, which is good news. Whether he is ready I will wait and see.

'I will just wait today and tomorrow. We will do a fitness test tomorrow and then we will see how he is.'

Midfielder Wes Hoolahan has missed the last two games with a hamstring pull, but appears close to a return.

'He looks okay at the minute,' said Lambert. 'We will see how he is today but he looks okay.'

The risk factor is clearly the issue for Lambert: if he plays Holt and the problem returns, he could lose his leading scorer for the rest of the season – just when he needs him most. There is a balancing act, You just have to make the decisions that you think are right, that's all you try to do, to make the right decisions and whatever will happen will happen,' said Lambert, who acknowledged just how important the pair have been under his stewardship.

'Two massive players for us who have made a huge contribution to the club in the time I've been here,' he said.

'He (Holt) has been colossal for us, but if not, whoever plays has got an opportunity.'

There are options: on-loan Wolves striker Sam Vokes, Dani Pacheco, the in-form Simeon Jackson and even Chris Martin, who has been out for more than two months with a hamstring problem.

Vokes, who scored at Watford on Tuesday, would be vital should Holt miss games, but there is a danger he could be heading back to Molineux after Thursday's game at Ipswich.

Wolves boss Mick McCarthy has a shortage of fit strikers and has said he intends to recall Vokes after the initial 28-day loan period expires next Thursday.

'Sam is Mick's player really so you can't do anything when he is not your player,' said Lambert. 'The guy's come in and done great for us and scored the goal, which will do his confidence really good but that is the problem you have with loan players.

'It's Mick's prerogative because he's manager of Wolves and he has to do what is right for him. I have not had the conversation with him yet.'

Martin appears to be an unlikely candidate for tonight, and with Lambert trying to organise a behind-closed-doors friendly to help with his match fitness there is no pressure to throw him back in at the deep end.

Lambert also has midfielder Korey Smith available after he missed the game at Watford with an eye infection.

'We don't have to, because obviously Simeon's there, Sam is there and Dani's there so Chrissy, after not playing for two and a bit months is still there if we want to do it. If we want to throw him in I can do it.

'Simeon's on form at the minute and is scoring, which will do his confidence a lot of good.

'I have every belief in the lads that whoever plays will do well.'