Sam Allardyce wants him to become his “ugly bulldog”, but Jason Roberts appears determined to follow Benni McCarthy, his fellow striker, out of Ewood Park in January unless he can secure assurances of regular action.

After coming off the substitutes’ bench to score twice and keep Portsmouth, his former club, in trouble at the foot of the table, Roberts revealed he has turned into a moody character because of his lack of appearances.

Allardyce, the Blackburn Rovers manager, has conceded McCarthy may leave during the transfer window so he can secure a place in South Africa’s squad for the World Cup finals. Roberts, who has been forced to watch from the sidelines, too, is also considering his future.

“Will I still be here in January? I’ll have to see,” he said. “I’ve not been in the best of moods recently. All you can do is do the business when you get the opportunity.”

After Jamie O’Hara had given the visiting team an early lead, Roberts equalised within minutes of being introduced after half-time.

Ryan Nelsen, the captain, headed Blackburn ahead for the first time before Roberts added to Portsmouth’s problems towards the end.

Although Roberts is frustrated at his lack of chances this season, Allardyce believes that the player may have a future at Blackburn.

“He should be the ugly bulldog for me,” Allardyce said. “He won’t like me saying that, but he should be.

“He should be snarling and biting and snapping at centre halves all day. And when he is like that, he becomes unstoppable.”

After back-to-back wins in the Barclays Premier League and Carling Cup, it is back to the drawing-board for Paul Hart, the Portsmouth manager. His team’s failure to defend from set-pieces after half-time proved that their troubles are far from over.

“I haven’t seen whose mistakes they were, but we have got a team full of players who have played at international level,” O’Hara said.

Blackburn Rovers (4-4-1-1): P Robinson 5 — P Chimbonda 5, R Nelsen 7, C Samba 7, G Givet 6 — E-H Diouf 5 (sub: B McCarthy, 46min 6), B Emerton 6, S N’Zonzi 6, M G Pedersen 5 (sub: J Roberts, 46 8) — D Dunn 7 — F Di Santo 6 (sub: K Andrews, 84). Substitutes not used: J Brown, M Salgado, D Hoilett, N Kalinic. Booked: Chimbonda, Givet, Nelsen. Next: Bolton Wanderers (a).

Portsmouth (4-4-2): D James 6 — Y Kaboul 6, A Mokoena 6 (sub: Kanu, 78), A vanden Borre 6, T Ben-Haim 6 — K-P Boateng 6, M Brown 6, J O’Hara 7, M Wilson 6 — F Piquionne 6, A Dindane 6 (sub: T Smith, 52 5). Substitutes not used: J Ashdown, M Williamson, H Mullins, N Belhadj, D Webber. Booked: Boateng, Brown, O’Hara. Next: Stoke City (a).

Referee: A Marriner Attendance: 23,110