Everton are sweating on the fitness of Fabian Delph after he picked up an injury in the goalless draw against Watford on Wednesday.
The midfielder has made a big impact since returning after spending four months on the treatment table.
The Toffees are unbeaten in the five games that Delph has featured in since overcome a thigh issue. They've accrued 11 points and are now two points above the Premier League relegation zone.
However, Delph picked up a setback in the 0-0 stalemate at Watford and was substituted for Allan in the 81st minute.
Frank Lampard admits the former England international will be a 'big miss' as Everton await news ahead of their clash against Brentford on Sunday.
The Goodison Park boss told the club's media team: “He's been great. He's a good player, a great lad, great in the dressing room, trains well, experienced, calmness and good quality.
“He's been a big plus for us and I don't know what the injury is. We will have to see what it is.
“He will be a miss because you need your big players in these moments and he's shown that.
“He's absolutely produced and helped the team.”